community structure, abundance and diversity of fish in a mexican coastal lagoon system

Estuarine and Coastal Marine &ience (1978) 7, 497-519

Community Structure, Abundance and Diversity of Fish in a Mexican Coastal Lagoon System

K. Warburton Department of Marine Biology, University of Liverpool, Port Erin, Isle of Man, U.K. Received II November 1977 and in revised form aq&nuary 1978

Keywords: fish; community; lagoon; seasonal variations; abundance; diversity; distribution; Mexico west coast

Regular beach seine hauls made during 1975-76 at a variety of sites within the Huizache and Caimanero lagoon areas produced a total of ++ fish species, representing 19 families. The anchovy Anchoa pananensis, the sardine Lile stolifera and the mullet Mugil curema were the top three dominants and comprised over 90% of the total number of fish caught. The abundance of both pelagic and demersal fish was greatest from November to March, with higher mean densities at H&ache than at Caimanero. Diversity and evenness were similar in both areas, being highest between April and October. Species richness was high between August and October at Caimanero but showed no distinct peak at Huizache. In an analysis of both areas combined, 41 out of a possible 23 I pairs of species were found to be positively associated in terms of frequency of occurrence. The three major species clusters identified in the analysis (characterized respectively by gerrid-centropomid species, gobies and pelagic forms) corresponded closely in terms of species composition with those given by a division by feeding habit into (I) omnivores and/or primary consumers, (2) detritivores and (3) planktivores. Species groups most typical of the different sampling areas were defined, fauna1 similarities within stations being connected both with habitat type (especially substrate) and with geographical location. The top carnivore of the fish community, the catfish Galeichthys caerulescens, was the only member unassociated in the combined analysis with any other species, although at Huizache it appeared to be affiliated with the gerrid-centropomid group.

Introduction

Like others in the area, the Huizache-Caimanero lagoon system of northwest Mexico supports an important penaeid shrimp fishery. Young shrimp enter the lagoon and, after a growth phase, are caught near artificial exit barriers as they migrate back to the ocean. Recent and continuing work (see Edwards, 1977), aimed at the eventual improved manage- ment of the fishery, has elucidated aspects of shrimp biology, but an appreciation of the causes of fluctuations in shrimp production necessarily involves the investigation of the whole lagoon ecosystem (Edwards SC Bowers, 1974; Edwards, in press). In this connection an understanding of the extent of the effects of competition and predation, notably by fish, crabs and birds, on the shrimp populations is of great importance. Other than species lists

Present address: D.A.F.S. Marine Laboratory, P.O. Box 101, Victoria Road, Torry, Aberdeen AB9 8DB, Scotland.

497 0302-3524/78/120497+23 $01.00/O @ 1978 Academic Press Inc. (London) Ltd.

498 K. Warburton

Figure I. A map of the H&ache-Caimanero lagoon system. The mean minimum limits of the lagoon (late dry season) are dotted. B. Botaderos; C, Caimanero canals; G, Las Garzaa; L, Caimanero lagoon edge; 0, Tapo Ostial; T, Caimanero tapo.

and a localized study of the Rio Baluarte estuary made by Amezcua (in press), very little information on fish population ecology is available. The present report is the first quanti- tative and comparative appraisal of the abundance, diversity and seasonality of separate lagoon fish communities from this region. Further results (Warburton, in preparation) describe aspects of the population and trophic dynamics of selected important species, with the final intention of assessing the impact of fish upon the shrimp industry.

This study was undertaken as a part of a cooperative project involving the National Autonomous University of Mexico (UNAM) and the University of Liverpool. British funding was provided by the Ministry of Overseas Development.

Study area

The Huizache-Caimanero lagoon system (22”50’-23’5’N and 1o6oo’-1o6~15’W) is shown in Figure I. A double lagoon occupies the area between two rivers, and is connected to them by two narrow winding channels (termed ‘esteros’). During the wet season (from June to September) freshwater enters the lagoon via land runoff, direct precipitation and through the esteros from the rivers, while from October onwards, the esteros act to conduct sea water from the ocean in compensation for the effects of evaporation and reduced precipitation. During the period of this study, air temperatures ranged between 18.3 “C (February 1975) and 27’9 “C (August 1975).

In order to monitor the fish communities in areas important to the shrimp fishery, permanent collecting sites were established close to three of the five ‘tapos’ or barriers which prevent the passage of shrimp migrating along the esteros. These were at Botaderos (Station B) and Tapo Ostial(0) in H&ache, and at Tapo Caimanero (T) (Figure I). Addi- tional stations were set up in the canal system (C) and close to the usual dry season margin

Fish in a Mexican coastal lagoon 499

of the lagoon (L) at Caimanero, and at the lagoonward end of the Huizache ester0 (Las Garzas, Station G). At each station the bottom substrate was of line mud of variable organic content. The density of mangroves lining the edges of the esteros was especially great at the Huizache stations. The canals at Caimanero are dredged from time to time and have artificial embankments. The Caimanero lagoon station was characterized by almost flat stretches of mud which shelved from low banks sparsely populated with salt-marsh vegetation.

Materials and methods

Fish communities were sampled regularly between February 1975 and May 1976 with a beach seine net having the following dimensions: wings, 21.71 x 2.83 m; bag length, 8.27 m; bag max. ht, 4.94 m; bag mesh, 1.0 cm. Area covered per haul was approximately 425 ma. No hauls were made at Botaderos or at Caimanero tapo between July and November (wet season) because of the flooding of all suitable beaches and the formation of unworkable deposits of mud, and seine samples could be taken at the Caimanero lagoon station only during the rains and until January, due to drying out. A range of cast nets were also used, but in this paper cast net data are included only in order to complete the species list and to provide total catch data for each family. Because of a much-obstructed bottom and beach at Tapo Ostial, only cast netting was possible at this station. At the time of capture, fish were preserved in 10% formalin, and records were kept of water temperature and salinity. Collected fish were sorted by species, counted, measured and weighed in the laboratory. All species authorities are given in Table I. Estimates of fish density in Table 2 are minima since no correction for net efficiency was made.

Species diversity was calculated using Simpson’s (1949) function based on probability theory :

D=I-I/N(N-I) z, N, (N,-I)

where D is diversity, N is total number of individuals, and N, is the number of individuals in a given species j.

The evenness component of diversity may be calculated by expressing the total number of individuals N as follows :

N=S(N/S)+r

where S is the number of species and (N/S) is the integer part of N/S (see also Pielou, 1969). Maximum diversity is attained when S-Y species have (N/S) individuals and I species have (N/S)+1 individuals, so that

Evenness is given by DID,,,,,, values ranging from o to I, where all species are equally abundant.

The species richness element of diversity (R) was expressed by

R=(S--)/log N (Margalef, 1969).

For the analysis of association (by occurrence) between species, those species occurring in less than 10% of the samples were eliminated, reducing the usable number to 22. Each possible combination of two species was tested for association by means of the contingency table technique of Hopkins (1957). The Huizache, Caimanero and combined data were treated separately. The efficiency of such a presence/absence technique has been asserted by many workers, including Ivimey-Cook & Proctor (1966), Webb et al. (1967) and Briand

TABL

E I.

Num

eric

al

abun

danc

e of

fis

h sp

ecie

s in

se

ine

colle

ctio

ns

from

di

ffere

nt

stat

ions

, H

uiza

che-

Cai

man

ero

1975

-197

6

Stat

ions

H

uiza

che

Cai

man

ero

B G

T

C

L

Fam

ily/s

peci

es

Tota

l N

N

/hau

l To

tal

N

N/h

aul

Tota

l N

N

/hau

l To

tal

N

N/h

aul

Tota

l N

N

/hau

l

Elop

idae

El

ops

afin

is

Reg

an

Clu

peid

ae

Dor

osom

a sm

ithi

Hub

bs

and

Mille

r Li

Ze rt

olife

ru

(Jor

dan

and

Gilb

ert)

Engr

aulid

ae

An~h

ovia

m

acro

lepi

dota

(K

ner

and

Stei

ndac

hner

) An

thoa

pa

nam

ensi

s (S

tein

dach

ner)

A.

mw

deol

uide

s (B

rede

r) C

hani

dae

Cha

ms

chan

os (

Fors

kal)

Ariid

ae

GaI

eich

thys

ca

erul

esce

ns (

Gun

ther

) Ar

ius

liroi

xs

(Bris

tol)

Hem

irham

ihid

ae

’ H

ypor

ham

phus

un

ifasc

iatw

(J

orda

n an

d G

ilber

t) Po

ecilii

dae

P~ec

iliopJ

is

c.f.

gruc

iZis

(H

ecke

l) Po

ecilia

sp

heno

ps V

alen

cien

nes

Athe

rinid

ae

Thyr

inop

s cr

ystu

llinn

(Jor

dan

and

Cul

ver)

Cen

tropo

mid

ae

Cen

tropc

mus

ni

gres

cens

Gun

ther

C

. ro

b&o

Jord

an

and

Gilb

ert

Car

angi

dae

Car

anw

hi

ppos

(Li

nnae

us)

Olig

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es

mun

dus

(Jor

dan

and

Star

ks)

0.

suw

u (B

loch

an

d Sc

hnei

der)

Sele

ne b

rew

oorti

i (G

ill)

S. o

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edii

Lutk

en

Trac

hino

tus

kenn

edyi

St

eind

achn

er

3 2 43

36

srgt

36 2 13

2560

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6

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33

3'54

34

21

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07

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62

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77

2488

6 16

59.0

7 53

67

412.

85

96

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77

0.1-

j

1’00

61

4'

70

I 96

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38

45

45

3.00

3.00

5'92

0.69

42

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0.08

70

4'67

138

9.20

2 0.

13

30.5

0 23

4.62

14

94

47

3.62

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ast

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only

46

3'54

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13

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156

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97

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t ne

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2 8 53

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TABL

E I-c

ontin

ued

Fam

ily/s

peci

es

Stat

ions

H

uiza

che

Cai

man

ero

- B

G

T C

L

-

Tota

l N

P\

T/ha

ul

Tota

l N

N

/hau

l To

tal

N

N/h

aul

Tota

l N

N

/hau

l To

tal

N

N/h

aul

Lutia

nida

e Lu

tjanu

s no

sem

fasc

iatu

s G

ill G

errid

ae

Ger

res

cine

reus

(W

alba

um)

Euge

rres

axilla

ris

(Gun

ther

) D

iapt

enrs

pe

ruvi

anus

(C

uvie

r an

d Va

lenc

ienn

es)

Euci

nost

omus

ca

lifor

niie

nsis

(G

ill)

E.

sp.

Pom

adas

yida

e Pa

mad

asys

le

ucis

cus

(Gun

ther

) P.

m

acru

cant

hus

(Gun

ther

) Sc

iaen

idae

C

ww

scio

n xa

nthu

lus

Jord

an

and

Gilb

ert

%cr

of~o

gon

ecte

nes

Jord

an

and

Gilb

ert

Mug

ilidae

M

ugil

ceph

alus

Li

nnae

us

M.

cure

ma

Cuv

ier

and

Vale

ncie

nnes

G

obiid

ae

Gob

iom

orus

m

acul

atus

(G

unth

er)

Dor

mita

tor

lutif

rons

(R

icha

rdso

n)

Eleo

tris

pict

us

Rne

r an

d St

eind

achn

er

Gob

ione

llus

sagi

ttula

(G

unth

er)

G.

mic

rodo

n (G

ilber

t) M

icro

gobi

us

mira

flore

nsis

G

ilber

t an

d St

arks

Bo

thid

ae

Cita

richt

hys

gilb

erti

Jenk

ins

and

Ever

man

n So

leid

ae

Achi

rus

maz

atla

nus

(Ste

inda

chne

r) A.

pan

amem

is

(Ste

inda

chne

r) C

ynog

loss

idae

Sy

mph

urus

at

ricau

dus

Jord

an

and

Gilb

ert

5

138

438 6 I

20 6

62: 14

1.

08

17

1.31

5 0.

38

II 0.

85

59

4’54

6 0.

46

7 0.

54

24

I .6

0 71

0.38

10.6

2

33.6

9 0.

46

0.08

I.54

0.46

0.15

47’9

2

90

6.00

21

I ‘4

0 19

I

‘27

II 35

216 8

7096

46

75 I 7

104 3

0.73

40

2.33

28

14’4

0 15

3

0’53

5

473’

07

247

3’07

55

5

‘00

9 0.

07

0.47

6

6.93

66

0'20

18

3 3 I5

I.15

Cas

t ne

t on

ly

61

4.69

2

0.15

2

0.15

Cas

t ne

t on

ly

3.08

2’15

71.7

7

0.38

19

.00

4’23

0.

69

0.46

5.

08

14.0

8

0.23

5.46

C

ast

net

only

I 0.

08

I 0.

06

I9

I.19

‘3

0.81

2

0.13

I

0.06

I 0.

17

18

3.00

59

9.83

3

0.50

2

0’33

27

i:

6

155 4 3 I 4

36

82

1.69

2'00

5.

00

0.38

9.69

0.25

0.

19

0.06

0.

25

2.25

5’13

I9

3’17

28

4.67

I

0.17

I 01

17

105

17’5

0

7 “‘7

22

3

-67

55

51

3’19

27

9’17

4’50

502 K. Warburton

TABLE 2. Mean densities of fish at different stations (from seine net data)

Stations

Huizache Caimanero

B G T C L

Pelagic Total number 15,088 28,454 8577 6933 1709 Number haul per II60 1896 659 433 284 Number m* per 2-73 4.46 1’5.5 1’02 0.67

Demersal Total number 2029 8072 1271 652 407 Number haul per 156 538 97 40 67 Number ma per 0.37 1.26 0.23 0’10 0.16

Combined Total number r7,rr7 36,526 9848 7585 2116 Number haul per 1316 2435 757 474 352 Number per ma 3’10 5’73 I .78 1’11 0.83

Ratio N pelagic : N demersal 7’4 3’5 6.7 10.6 4’2

Number of hauls r3 I.5 13 16 6

(1976). Association diagrams were constructed by selecting the pair of species displaying the strongest positive association (highest x2 value), linking each in turn through the strongest remaining associations with further species, and continuing the process until all species were included. As a comparison, dendrograms were constructed according to the standard nearest neighbour or single link fusion sorting method (Williams et al., 1966). The two methods were considered complementary, since the former stresses directional species- species affinities and uses the most significant association information for all species, whereas the latter delineates species-group and group-group relationships in the erection of a hierarchy.

Collecting areas were characterized according to the relative dominance and ubiquity of the common fish species. All species taken at any station were ranked by frequency of collection, and the rank concordance of species was examined within each possible pair of stations. Numbers of species showing widely separate rankings were totalled for each station pair and used to erect an index of station similarity, while those species consistently displaying high rankings at a given station were selected as being most characteristic of that area. Where there was an obvious dominance of one or more stations in terms of the absolute numerical abundance of any species, this information was also used in station characterization.

Results

Variations in water temperature and salinity throughout the year are plotted in Figure 2.

Temperature remained within the range 20-34~ C, there being little difference between the stations. However, when compared to the remainder, stations B (Botaderos) and T (Caimanero Tapo) displayed characteristics of deeper bodies of water, taking comparatively longer to warm up as the hot season progressed and remaining warmer during the cooler


40. HuizacJw

30. ...... Tapa Oatial

20.

$ IO.

2

f 4: Caimanera z Ta$ioknanero

c” 30.

.. ” Logoon edge

20.

IO.

40 t

30

20 I

101

Caimanero

77

1 . . . * I. 1. . . FR - LR c

‘FMAMJJASONDJFMAM

I975 I976

Figure z. Records of the salinity and water temperature at the various collecting stations during the study period. The timings of the first rains (FR), last rains (LR) and a cyclone (C) are indicated.

months. The pattern of temperature change was not identical during the springs of 1975

and 1976. Salinity showed a sharp decline (from fully saline to almost zero) at all stations immediately following the onset of the rains in June 1975, after which time there was a slow recovery to full salinity by about March. A sudden drop in salinity at Huizache between January and March 1976 was due to a temporary artificial diversion of the Rio Presidio, made to maintain lagoon contact with the sea during the dry season.

A total of 44 species of fish, from 19 families, were identified during the survey (Table I).

In terms of numbers of species, the Gobiidae were best represented (6 species), followed by the Carangidae (6, but none particularly common) and Gerridae (5). The numerically dominant species was An&a panamen.& (anchovy), followed by Lile stolifera (sardine) and Mugil curemu (mullet), these three making up over 90% of the total catch. However, the halfbeak, Hyporhamphus unifascitus, was the third most dominant species at Botaderos, and the total numbers of mullet were much inflated by a large catch of juveniles (6643 individuals) at Las Garzas on 17 March 1976. Fish abundance was greatest at Las Garzas followed by Botaderos and Caimanero tapo, canals, and lagoon (Table a) respectively. Numbers rose by two factors of ten from a low in late spring to a maximum between Nov- ember and March in both lagoon areas (Figure 3), this trend being still evident when the

504 K. Warburton

f 3 3

4.l

3.

2.

I .

Ol

3.

2.

I .

Oh

(a) - LOSGmoS --- Boladsras

IAMJJASONDJFMAN

I 975 I 976

Figure 3. Graphs showing total numbers of fish taken per seine haul at Huizache (a) and at Caimanero (b) during the study period.

(0) -Las6alzas -Bolabas

Figure 4. Graphs showing total numbers of fish, minus the numbers of pelagic pIanktivorous forms (families Clupeidae, Engraulidae and Hemirhamphidae), taken per seine haul at H&ache (a) and at Caimanero (b) during the study period.

Fish in a Mexican coastal lagoon 50.5

generally large numbers of small pelagic planktivorous species (Clupeidae, Engraulidae and Hemirhamphidae) were neglected (Figure 4).

The number of occasions when representatives of a family were caught individually compared as a ratio with the total number of occasions when the family was represented in a catch, showed a linear decline as the total number of occasions increased. The families containing most of the larger common carnivores in the lagoon system (Ariidae, Sciaenidae, Centtopomidae, Pomadasyidae, Soleidae, Gerridae) displayed close similarities in terms of solitary occurrence (3o--50~/~ of total number of occasions recorded). Notable exceptions to the above correlation, other than some families with a very low abundance, were the pelagic groups referred to above, plus the Poecilidae and Atherinidae. For these, the relative frequency of single individuals remained at a lower level than for other families (I 5-25 %)

regardless of the total frequency of occurrence, this no doubt being a reflection of the higher sociability of the groups concerned (Figure 5).

50 I 00 I 50 T

Figure 5. Graph showing the relative sociability of fish families as indicated by catch data. S is the number of occasions when solitary members of a family were caught, and T the total number of occasions when the family was represented in a catch. From seine and cast net data. AR, Ariidae; AT, Atherinidae; BO, Bothidae; CA, Carangidae; CE, Centropomidae; CH, Chanidae; CL, Clupidae; CY, Cyno- glossidae; EL, Elopidae; EN, Engraulidae; GE, Gerridae; GO, Gobiidae; HE, Hemirhamphidae; LU, Lutianidae; MU, Mugilidae; PC, Poecilidae; PO, Poma- dasyidae; SC, Sciaenidae; SO, Soleidae.

Community seasonality, as expressed by the Simpson’s D, evenness and species richness indices, was similar at all stations. Diversity was highest between June and October, although high also in the earlier collections from Huizache (Figure 6). After a fairly abrupt fall in October, it declined, but with a series of wide perturbations, to a low point in April. Caimanero tapo (2’) was the only station not exhibiting such fluctuations, which in the case of the Huizache stations G and B appeared mutually complementary. Overall, diversity was not markedly different between Huizache and Caimanero. The evenness component varied in a manner very similar to diversity. Species richness rose at Caimanero from a low in April to a peak between August and October, but no trend, other than a sustained gentle decline, was obvious at Huizache, where species richness was greatest at Station B. The greatest numbers of species were recorded at Huizache between September and December,

506 K. Warburton

(a) - Tapo

I a ----Canal! .“““. wl@J

‘..I

0, ..’

:: . 0, . . .

1975 1976

I (b) - Las 6arza

I ,o c --- @@adsras

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I ,o --? “I$ w

0 . . ‘. ‘. . “‘. IO -

8.

4- 2-

I. . . . . . . . . . . . . oYAMJJASONDJFMAM

1975 1976

Figure 6. Variations in species diversity (D), evenness (E) and species richness (SR) at Huizache (a) and at Caimanero (b) during the study period.

Fish in a Mexican coastal lagom 507

508 K. Warburton

t t $ I I I I I I I

510 K. Warburton

and at Caimanero between October and March. Lowest numbers were obtained at both from April to June.

In each of the three analyses of species association, the total number of species pairs was 231. The numbers of significant associations (P<o*og) were as follows: Huizache, 14;

Caimanero, 35 ; combined, 41 (positive association), and Huizache, 7; Caimanero, 7; combined, 5 (negative association). Of these, those significant at the 1% level numbered 4, II,

and 14 (positive) and o, o, and 2 (negative) respectively (Tables 3-5). Since chance will dictate that 231/20=16 pairs should be significantly correlated at the 3% level, all three sets of results gave numbers of positive associations in excess of those expected on a chance basis. The consistently low frequency of negative associations was probably due to the reduced numbers of some species (Agnew, 1961). Strength of association may vary with the total number of samples (Hurlbert, 1969), and is most likely the reason for the lower frequency of significant associations recorded from Huizache, where fewer data were available. The results from the analysis of the combined data [Figure 7(a)] suggest the existence of at least three groups of species, which also have taxonomic or ecological affinities. One may be termed the ‘Gerridae’ group (henceforth termed group GER), since Gerres, E&no- storms and Diapterus are all closely associated. Other members of the group, which is well separated in the association field from other species, are Poeciliopsis and Centropomus. Adjacent to this group are the five goby species (group GO), which, although closely inter- related, also share affinities with Micropogon and Thyrinops. Adjacent to the latter species, one may then make out a group (PLA) of small pelagic planktivores comprising Anchoa spp. and Lile. The existence of a multi-dimensional association field is implied, since the latter group abuts onto the first, group GER. In addition, the presence of relatively weak side- associations suggests that the halfbeak Hyporhamphus, the sole Achirus and the mullet Mugil curema are to be considered peripheral members of group GO, and that the larger carnivores Cynoscion and Pomadasys are affiliated with group PLA. The remaining mullet (M. cephalus) is more closely associated with Poeciliopsis and group GER. The only species not exhibiting any significant association with others was the most common large carnivore, the catfish Galeichthys, which instead was involved in three of the five significant negative associations (with Gobionellus microdon, Achirus and ikf. cephalus).

H S l

.--- --- ---.

1 i VIP

Species

-: I

I G-

r------ I

Fish in a Mexican coastal lagoon 5x1

(b)

12

8

I J E 0 l A

N;P

Figure 7. Association diagrams for the twenty-two most common fish species. Level of horizontal lines reflects degree of positive association of adjacent species; the connections vary in length so as to accommodate side-associations. Diagrams were constructed by selecting most significant association sequentially. Dashed lines (a) indicate important cross-associations: the diagram should be visualized as three-dimensional, with G. cinereus linked to D. per&anus directly. Side associations (unshaded) are species or species chains connected unidirectionally with the remainder. (a) Combined data from Huizache and Caimanero; G. caerulescens unassociated with other species. (b) Caiman ero data; A. panamensis and G. caerulescens both unassociated. (c) Huizache data. A, Lile stolifera; B, Anchoa pad; C, An&a mwuleoloiaks; D, Galeich&ys caerulescens; E, Hyporhamphw unifasciatus; F, Poeziliopsis c.f. gracilis; G, Thyrinops crystallina; H, Centropomus robalito; I, Gerres cinereus; J, Diapterus peru&nus; K, Eu&ostomus sp.; L, Pomaakys macracanthus; M, Cynoscion xunthulus; N, Micropogm ectenes; 0, Mugil cephalus; P, Mugil curema; Q, Gobiomorus maculatus; R, Dormitator latifions; S, Gobionellus sag&da; T, Gobionellus mkrodon; U, Microgobius mirafloreti; V, Achirus mazatlanus. 0, gerrid species; W, gobiid species; A, pelagic planktivorous species.

512 K. Warburton

TABLE 6. Characterization of collecting stations in terms of the fish fauna. *Characteristic species as indicated by comparison of species frequency ranks for each station. I, 2, etc., rank order of stations by relative total abundance (where there is obvious station dominance: see Table I)

Species Stations

B G T C L

E. aJinis L. stolife*a A. macrolepidota A. panamensis A. mudeoloides G. caerulescens H. unifasciaius P. c.f. gracilis P. sphenops T. crystallina C. nigrescens C. robalito Oligoplites spp. G. cinereus D. peruvianus E. californiensis P. macracanthus C. xanthulus M. ectenes M. cephalus G. maculatus D. latifrons E. pictus G. sagitulla G. microdon M. miraftorensis A. mazatlanus

*I I 3 2

I

2

3

*I

I

2 I

3 I

*2 *2

+3

*2 *3 l 2

I

I

I 2 l 1

*I

3

*2 * I

I

*1

3 *

*3 I

I

2 * * ‘3

*2 *2

I *I

I +2

2 *I

I

*2 +I

*2 2= I

*2=

*2

2 2

3 3 I

*I

*I

2 2

*3 *

At Caimanero [Figure 7(b)], a similar pattern emerged, except that Hyporhamphus was closer to group GER, Poeciliopsis and M. cephaZus were more closely associated with group GO, and the comparatively weakly bonded group PLA was dispersed: the anchovy, Anchoa panamensis, together with Galeichthys, did not display any significant associations. At Huizache, group GER remained discrete, embracing Hyporhamphus and also Galeichthys, but group GO split to accommodate group PLA [Figure 7(c)]. Dendrograms constructed by way of single link agglomerative sorting (Williams ei al., 1966) showed essentially the same species clusters, except that chaining effects tended to obscure more precise relationships between accessory species and the major groups (Figure 8).

The relative occurrence of fish species at various stations was used to characterize the coIIecting areas in terms of the fish fauna. Lile stol#era, Anchoa panamen.&, Genes cinereus, and Mugil curema were more characteristic of H&ache, while Microgobius miraJlorensis, Achiws mazatlanus, and Poecilia sphenops were more abundant at Caimanero. Dorosom and Chants were found only in the former system, and Olsgoplites and Symphurus only in the latter. Table 6 indicates that CentropomuF spp., D. pe~uvianus, H. un@.&atus, and E. ajinis

were most characteristic of Botaderos; D. rclti’ons and M. ectenes of Las Garzas; A. maxat- laws of Caimanero tapo; and C. xanthdus and G. microdon of Caimanero lagoon. The comparison of rankings of species by their frequency of occurrence in hauls from the various stations suggests that the stations of Caimanero tapo and Las Garzas were the closest in


.O.lO

-005

.OOl Yi

i M ” : L H 1 R P n l

‘i----i ====---l (b)

r J r

L c M A S U P A A smm

Species

N V-K l

1

1 S H

L F J

a

Figure 8. Dendrograms illustrating species and group associations; agglomerative, ‘nearest neighbour’ sorting. a, Combined data; b, Caimanero data; c, Huizache data. Details as Figure 7.

514 K. Warburton

TABLE 7. Fauna1 affinities of collecting stations

Stations involved in comparison

Total no. displaced species ranks in comparison Similarity rank

G T T C B L G C C L G L T L B G B T B C

ii

I

2

8

9 4 IO 5 IO

II I2 i

15 9 I5

terms of community composition, with the canal station closely associated with both. Botaderos and the Caimanero lagoon station, especially the former, were comparatively distinct from the rest, although mutually similar (Table 7).

Discussion

Most fish found in estuaries and coastal lagoons use them as areas for feeding and growth, since they provide protection from predators and ensure high food availability (Gunter, 1938; McErlean et al., 1973). In the case of the Huizache-Caimanero complex, most of the species penetrating the esteros were represented largely as juveniles, although the size ranges of a few (e.g., Gakichthys, the poecilids, Mugil spp., most gobies and Achirus) implied that they are resident or commonly enter as adults.

Of the ten dominant species, two are largely resident forms, at least six use the lagoon as a nursery ground and growth area, at least five feed as adults in and around the estuary, and one is primarily a fresh water species (Table 8) [ see Gunter (1956), McHugh (1961) and Alvarez (1970) for ecological classification]. In common with results from other similar

TABLE 8. Dominant fish species in three lagoon environments

Rank Rio Baluarte Estuary Huizache-Caimanero (Amezcua, in press) (this study)

I

2

3 4

i

;: 9

IO

L. stolifera (F/G) An&a panamensis (F/G) Anchoa panamensis (F/G) L. stolifera M. curema (SW M. curema :E!g’ G. caerulescens H. unifatciatus A. mazatlanus IY)

W C. robalito (F/G)

D. peruvianus D. peruvianus 63 Eucinostomus spp. g; M. ectenes P. macracanthus C. gilberti K)

T. crystallina IFiF; G. micro& uv

C. hippos (F) G. cinereus W

Agua Brava (Carranza & Amezcua, 1971;

hlCXLli3, 1972)

A. liropus C. robalito G. caerulescens 0. mundus A. mundeoloides L. stalifera Gem3 spp. M. curema P. macracanthus M. ectenes

M -Marine

iii -Feeding as adults in estuarine area -Using estuary/lagoon as nursery ground and growth area

R/SR -Resident in lagoon/seasonal resident FW -Primarily freshwater form


studies [see Allen & Horn (1975)] there was a high dominance of a few species low in the food chain: Anchoa panamensis, Lile and Mugil curema together comprised over 90% of the total number of fish sampled. Competition between the top dominants is probably kept to a minimum by varying habitat preferences and differences in feeding habits, since Mugil is a detritivore, anchovies feed largely on phytoplankton and sardines generally prefer zoo- plankton (Lowe-McConnell, 1977).

Forty-four species of fish, from 19 families, were recorded during the course of this work. More species (32) were taken at Botaderos, the station closest to the ocean, than at any other. A total of 57 species, from 26 families, have recently been reported from the estuary of the Rio Baluarte, which marks the southernmost limit of the Huizache-Caimanero system, and of those, 12 species were considered to be only occasional visitors from the ocean (Amezcua, in press). Similarly, 71 species representing 31 families were recorded by Amezcua (1972) from the Agua Brava system, ca. 43 km south east of the Baluarte. Fifteen species were represented by one individual only, and progressively fewer species were observed in moving towards the lagoon. The rigours of lagoon conditions are such that less than 15% of the fish species known from this area of the Gulf of California penetrate the local lagoons (Carranza, 1970). Numbers of species comprising similar communities on the Atlantic coast of Mexico are comparable to those quoted above, studies of the lagoons at Tamiahua and Alvarado in Veracruz having yielded 56 species (from 31 families) and 60 species (from 29 families) respectively (Resendez, 1970; 1973).

The relative dominance of many fish species appears to differ between the seaward (estuarine) and estero/lagoon areas. Lile, an estuarine genus, was dominant at Boca de Chametla (the Baluarte river mouth near the oceanic end of the Caimanero estero) (Amezcua, in press), while in this study, Anchoa was more abundant. Of interest is the difference in the relative abundance of these fish at Botaderos and Las Garzas, Anchoa being much more dominant nearer the lagoon. The catfish Galeichthys, the sole Achirus and the burro Poma- dasys are also more typically estuarine forms (Table 8). Evidence that the freshwater influence on the lagoon environment is quite strong is provided by the fact that Dorosoma, Chanos, Poeciliopsis c.f. gracilis, Poecilia and Microgobius were recorded from the inner areas but not from the estuary: Dorosoma and Microgobius are known to exhibit a wide salinity tolerance (Alvarez, 1970), and most of the freshwater poecilids were obtained between August and December when salinity was relatively low. Poecilia and Microgobius, and also the highly euryhaline Gobiomorus and Dormitator, are very scarce at Agua Brava (Carranza & Amezcua, 1971), suggesting hydrological differences between the two systems. Also relevant are the statements of Carranza (1970) and Carranza & Amezcua (1971) that although not numerically abundant, Elops afinis is very common in Huizache-Caimanero, and the fact that, following work in 197475, Edwards (in press) includes this species as one of the 18 most noteworthy in the system. Since only five specimens were taken during this study (including three close to the ocean at Botaderos), this perhaps implies the existence of variations in abundance of a longer term nature than the period covered here. The possi- bility of long term community periodicity is highlighted by the work of McErlean et al. (1973) and Hilhnan et al. (1977), and the fact that, at Huizache-Caimanero, hydrological parameters such as salinity are known to exhibit wide variations from year to year (c.f. Gomez-Aguirre, 1974).

According to Amezcua (in press), total fish densities at Boca de Chametla in 1974-75

were ca. 2 individuals mm2, except for restricted periods around November and March, when peaks of ca. 8 me2 and ca. 6.5 mm2 respectively were recorded. These figures compare with the mean value of 2.7 mm2 for the inner system quoted here, and with an absolute

516 K. Warburton

maximum of 18.3 m-a (at Las Garzas in March). This period of high abundance of individuals and species appeared to be later in its timing and more sustained (from November to March) at both Huizache and Caimanero than in the estuary, where the only consistent rise in abundance common to several families (viz. Carangidae, Soleidae, Pomadasyidae, Sciaenidae, Centropomidae and Gobiidae) occurred between August and November. Levels of species diversity and evenness were, however, highest in the wet season in Huizache- Caimanero, such fluctuations probably relating to the seasonal migration of non-residents. The timing of the period of increased abundance coincides with one of high plankton density (Gomez-Aguirre, 1974) and may be linked to the reproductive cycles and ecological success of a relatively reduced assemblage of species; to a much greater extent than in the estuary, environmental stresses within the lagoon must be highest at the onset of the wet season and perhaps dictate that increased production and stability be realized only after a phase of accommodation to changed conditions. In the present case, the influence of salinity upon community parameters is most likely to be equal to or greater than the effects of temperature described by previous workers (e.g. McErlean et al., 1973 ; Allen & Horn,

1970 Fish densities, like those of plankton (Gomez-Aguirre, rg74), were higher at Huizache

than at Caimanero, especially at Las Garzas. Within Caimanero they were greater at the tapo than in other areas. Although the density of pelagic forms in all cases exceeded that of the demersal fish by a factor of 3.5-10.6, the latter are nonetheless important in regulating the diversity and abundance of other members of the benthos and providing opportunities for a fishery, as described by Oviatt & Nixon (1973). Density estimates from Las Garzas were comparable with those quoted by Edwards (in press) for the Huizache flats, and those from the Caimanero lagoon station with his Caimanero flat data. However, the figures for the canal station (1.02 and 0.10 individuals m- 2 for pelagic and demersal fish respectively) are markedly at odds with Edwards’ calculations of 8.14-10.70 and 18*12-150.50 m-2 for the same area, and agree more closely with his marisma estimates (0.16-7.53 and o-04- 2.55 mm2 respectively). There is thus some evidence for consistency in population density and for homogeneity of habitat, but also for perturbations from the norm in some areas. It may be significant that densities of pelagic fish were only 4.3-6.7 times greater in a mangrove area (Las Garzas) than at the Caimanero canal and lagoon edge stations, while for demersal fish the difference is larger (7’g--13’2 times). This probably reflects the greater dependence of the demersal forms on the substrate, which in mangrove zones provides a much richer food source. These conclusions accord with Edwards’ (1977) measurements at Caimanero of the respiration and combustible organic content of different lagoon substrates.

In terms of frequency of abundance, it proved possible to define three species associations, characterized respectively by gerrids-centropomids, gobies and engraulids-clupeids, and some inferences as to the possible ecological significance of these groupings may be drawn. The engraulid-clupeid associationisfundamentally one of pelagic species,while the demersal species were split between the gerrid and gobiid groups. Within the Gerridae, species tend to show a certain homogeneity in feeding habits (Prabhakara Rao, 1968; Yanez, rg75a) and members of the gerrid association are typically omnivores (Gerres, Eucinostomus, Poeciliopsis) and/or secondary consumers (Diapterus, Eucinostomus, Centropomus; in Huizache Galkichthys and Elops; c.f. Yanez, 19750). In contrast, genera of the gobiid complex (Dormitator, Gobi~us, Gobiodlus, Micro@ius, Achirus) are predominantly detritivorous (Carranza, 1969; Yanez, Igysa). Atherinids feed on both detritus and plankton (Ramirez, 1952;

Cervigon, 1966; Leim & Scott, 1966; Edwards, in press; Warburton, in preparation) and,


perhaps significantly, Thyrinops was directly associated with the pelagic as well as the gobiid group.

The analysis of separate results from Huizache and Caimanero suggested that the relative strengths of the associations varied with locality and dominance ranking established that the different groupings may to some extent be representative of an area. An important factor was the extent of marine influence. Thus, the station nearest the ocean (Botaderos) was characterized by the estuarine forms Hyporhamphus and Elops and a strong gerrid- centropomid influence, while the Caimanero tapo and lagoon stations displayed definite, though not identical, gobiid features. Because of these differences, it is likely that the gobiid group will be well represented in areas where the bottom is muddy and rich in organic detritus, while in contrast it is known that gerrid species prefer sandy bottoms, especially those close to the sea (Cervigon, 1966).

Within an association, species coexistence may be facilitated by a selective utilization of available food by the various species so that niche overlap is kept to a minimum. In this connection the differences in the feeding mechanisms of mullets, gobies and flatfish (gobiid group) and of anchovies and sardines (pelagic group) may be cited. The association of the two sciaenids Micropogon and Cynoscion with different groups may be related to size-specific feeding preferences, since most individuals of the former genus were juveniles and most of the latter adult or near-adult. Cynoscion is largely piscivorous, frequently taking sardines and anchovies (Carranza, 1969; Warburton, in preparation), and this may be an important factor contributing to its association with the pelagic group.

With reference to the families represented in the collections, the delimited associations comprise reasonably discrete taxonomic units; the Centropomidae and Poecilidae are both systematically close to the Gerridae, the combinations of Anchoa and Lile and of Cynoscion and Pomadas-ys each represent consecutive families, and the Gobiidae have closer affinities with the Mugilidae and Soleidae than with any of the other families. The large-scale adoption of detritus feeding by fish may therefore be a relatively late evolutionary development.

The catfish, Gakichthys, is by far the most important large predatory fish in the lagoon area. Although known to take other fish and large crustaceans, including penaeids, its feeding preferences are extremely wide (Carranza, 1969; Gonzalez, 1972; Yanez et al., 1975; Warburton, in preparation). Together with its ubiquity (Gonzalez, 1972; Yanez et al., 1975), this may be the reason for its general lack of association with other species. The association of Galeichthys with members of the centropomid-gerrid group at Huizache is supported by the observations of Gonzalez (1972), who ranked Centropomus and Diapterus I and 3 respectively in a list of species most often associated with the catfish, and may reflect its estuarine preferences, since discounting 60 small juveniles taken on 16 September 1975

at Las Garzas, more specimens were obtained at Botaderos than closer to the lagoon. It is interesting to note that five out of the six significantly negative associations involving Galeichthys were with members of the gobiid complex, despite the predominance of this group at Caimanero, where most adult cattish were caught. This phenomenon is more probably a product of micro-habitat preference rather than of prey discrimination, since gobies are readily taken by Galeichthys (Yanez et al., 1975; Warburton, in preparation). Since there exists an inverse relationship between the relative abundance of shrimp and mullet, ostensibly due to direct competition (Carranza, 1970; Yanez, 1975b), and given the association of both species of Mugil with the gobiid group at Caimanero, then increased concentrations of catfish or an impoverished gobiid fauna may be associated with high shrimp yields, and vice versa.

518 K. Wwburtm

Acknowledgements

The author is grateful to Dr A. Ramirez, Dr A. Ayala-Castanares and Dr A. Laguarda for support and the provision of facilities, to Professor E. Naylor and Mr A. B. Bowers for their help and advice, and to Dr I. Baker for local support. Particular thanks are due to Alfonso Rojas and Juan Valenzuela for their willing help and cooperation in the field, and to R. Campos, R. Chan Gonzalez, J. M. Melchor, D. Chavez and my wife Jeni for assistance in the laboratory. Financial support was provided by the Ministry of Overseas Development, London.

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community structure, abundance and diversity of fish in a mexican coastal lagoon system

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