diet diversity of jack and chub mackerels and ecosystem ... · la niña 2007 la niña . 1975-76 ....

Victoria BC, 06-11 March 2017

Ana Alegre1,2, Arnaud Bertrand2, Marco Espino1, Pepe Espinoza1,2, Teobaldo Dioses1, Miguel Ñiquen1, Iván Navarro1, Monique Simier2, Frédéric Ménard2 1Instituto del Mar del Perú, Esquina Gamarra y General Valle s/n, Chucuito–Callao. 2IRD, UMR-MARBEC/IFREMER/IRD/UM, Av. Jean Monnet, BP 171, 34203 Sète, France.

ICES/PICES, Symposium on Drivers of dynamics of small pelagic fish resources

Diet diversity of jack and chub mackerels and ecosystem changes in the Northern

Humboldt Current System: a long-term study

SSTºC variability (1875 – 2007)

The NHCS is affected by intense climatic variability at multiple scales (seasonal, interannual, multidecadal,...).

Intense and shallow oxygen minimum zone (OMZ) O2 concentration <0.5 ml l-1

High climatic variability Introduction Objective Metodology Conclusions Results

Diet diversity of jack and chub mackerels and ecosystems changes in NHCS

Ana Alegre Norza Sior

PICES-ICES 07/03/2017

Oxygen minimum zone

NHCS – Day situation Introduction Objective Metodology Conclusions Results




Oxygen minimum zone

NHCS – Night situation Introduction Objective Metodology Conclusions Results




Median primary

productivity

High fish productivity

Food does matter need to study the trophic structure and energetic transfer (Source: Chávez et al. 2008)

What is the secret for such high fish productivity? Introduction Objective Metodology Conclusions Results




Need to better understand the reason of this collapse

JM and CM distribution depends on food availability. need to better understand the spatiotemporal patterns of JM and CM diet composition.

Jack and Chub mackerel population decreased dramatically in the late 1990s

Introduction Objective Metodology Conclusions Results




We investigate the spatiotemporal patterns of Jack mackerel Trachurus murphyi and chub mackerel Scomber japonicus diet composition.

Objective Introduction Objective Metodology Conclusions Results




Time series diet of two species

29,158 stomachs 1973-2013

18,377 stomachs 1973-2013

Total stomachs 47,535

Data Introduction Objective Metodology Conclusions Results

Data recovered analyzed




INDEX OF CONDITION FACTOR (Kn)

13 dietary groups

STOMACH FULLNESS WEIGHT INDEX (FWI, in %) compare with Kruskal-Wallis and Wilcoxon rank sum tests

29,158 and 18,377 Stomachs

CORRESPONDENCE ANALYSIS to order the prey taxa richness per year

90 and 102 prey taxa Weight (%W)

Occurrence (%O)

BOOTSTRAP to compute the diet composition by year, distance to the shelf break and latitudinal zones

2 CART: MULTIVARIATE REGRESSION TREE: Group ~ Species + SSTA+Size + Z15ºC + Zones+DistShelf Group ~ Year + SSTA +Size + Z15ºC + Zones + DistShelf

Methods Introduction Objective Metodology Conclusions Results




Our study question this: we found overall higher percentage of fish

(especially Engraulidae ) in CM (29%) than in JM (19%).

Medina and Arancibia 1998: JM selects much larger prey than CM.

JM

1

Chub mackerel Jack mackerel

Introduction Objective Metodology Conclusions Results Comparative diet

The first split of the regression tree

separates the 2 species




0%

20%

40%

60%

80%

100%

[-86.8, 0.0] [1.0, 26.1] [26.2, 63.9] [64.0, 912.2]

% W

eigh

t

Distance Shelf (km)

Cephalopoda Copepoda Zoea larvaeEuphausiidae Pleuroncodes monodon Others CrustaceaUrochordata Engraulidae MesolpelagicsCoastal fishes Others Teleostei Eggs and larvae TeleosteiOthers

0%

20%

40%

60%

80%

100%

[-86.8, 0.0] [1.0, 26.1] [26.2, 63.9] [64.0, 912.2]

% W

eigh

t

Distance Shelf (km)

Cephalopoda Copepoda Zoea larvaeEuphausiidae Pleuroncodes monodon Others CrustaceaUrochordata Engraulidae MesolpelagicsCoastal fishes Others Teleostei Eggs and larvae TeleosteiOthers

Jack

m

acke

rel

Ch

ub

m

acke

rel

The shelf break appears to be a biogeographic barrier

(Ballón et al. 2011) (Gutiérrez et al. 2008) Distance coast (nm)

P. m

onod

on B

iom

ass

Introduction Objective Metodology Conclusions Results Distance to the shelf break changes

Shelf break




Oceanic prey (euphausiids) dominated where the shelf is narrow (North and South). Coastal prey (squat lobster and anchovy) are more important in Central Peru where the continental

shelf is larger The shelf break extend can thus be an important factor

Jack

m

acke

rel

Ch

ub

m

acke

rel

Introduction Objective Metodology Conclusions Results Latitudinal changes




Hypothesis Exceptional El Niño events affect all marine ecosystems components (e.g. Barber and Chavez, 1983; Arntz and Tarazona, 1990) including JM and CM populations (Arcos et al., 2001; Bertrand et al., 2004b; Gerlotto et al., 2012).

Jack

mac

kere

l C

hub

mac

kere

l

El Niño 1982-83

El Niño 1997-98

La Niña 2007

La Niña 1975-76

La Niña 1999

No evidence of strong interannual effect of ENSO (El Niño and La Niña). Question the results of Sanchez and Muck (1987) based on few data and confirm the findings of Espinoza and Bertrand (2014) on anchovy diet

Jack mackerel

Introduction Objective Metodology Conclusions Results Interannual changes




The first split of the regression tree separates two time periods

Jack mackerel data

Condition factor before 2000 = 0.96 ± 0.11 - since 2000: 1.05 ± 0.10 (signif. diff.)

Introduction Objective Metodology Conclusions Results Decadal changes

Temporal shift




1972

1974

1976

1978

1980

1982

1984

1986

1988

1990

1992

1994

1996

1998

2000

2002

2004

2006

2008

2010

Years

0.00

0.15

0.10

0.05

-0.05

-0.10

-0.15

-0.20Euph

ausii

ds do

mina

nce

Euphausids Dominance in the ocean

Trend in euphausiids abundance off Peru (Ayón et al., 2011)

(Ayón et al., 2011)




Introduction Objective Metodology Conclusions Results Paradox

1980 1990 2000 2010

-1.0

-0.5

0.0

0.5

1.0

Year_1

s(Ye

ar_1

,8.9

)

Proportion Euphausiidae in the diet

Proportion Euphausiidae in the system

(Ayón et al. 2011)

Euphausiids dominated the JM and CM diet in a period when they were not very (Ayón et al., 2011). Why?

The Squat lobster is an easier and larger prey to capture than euphausiids

Proportion of Squat lobster in the system

(Gutiérrez et al. 2008)

• Both species Jack and Chub mackerel are opportunistic species with high plasticity. They feed on prey that are more accessible.

• During the 1970-1980s the euphausiids were not so abundant but they are easy prey for JM and CM

• Since the last decade the Squat lobster was present on the Peruvian coast.

Mean occurrence of Trachurus murphyi prey taxa per year.

First period before 1996 characterized

by low diversitiy

Second period from 1996 characterized by a larger number

of taxa

Introduction Objective Metodology Conclusions Results Richness




Hypothesis: Temperature and species richness are positively correlated (Frank et al., 2007)

Jack mackerel

Our results challenge such paradigm: prey diversity was higher during cold period than warm period.

Introduction Objective Metodology Conclusions Results Temperature vs. Richness

Low richness

Warm period

Chub mackerel

Low richness

High richness

Warm period

High richness

Cold period




The diet of these two species is dominated by zooplankton (then fish) (Konchina et al. 1996; Castro & Santana 2000); they are considered as opportunistic foragers (Konchina et al. 1981).

Introduction Objective Metodology Conclusions Results What did we know before?




• Both species are opportunistic and present a trophic overlap but surprisingly, JM does not seem more voracious than CM.

• Fish diet presented high spatiotemporal variability, the shelf break being a clear biogeographical frontier.

• Fish diet composition is not necessarily a good indicator of changes in prey biomass since prey accessibility and energy content does matter.

• Unexpectedly, El Niño events have a weak effect on stomach fullness and on the diet of CM and JM;

• Finally our results challenge the paradigm of positive correlation between diversity and temperature in the case of the NHCS.

Introduction Objective Metodology Conclusions Results What have we learned in this study about the diet of JM and CM?




Thank you!

¡Gracias!

Victoria BC, 06-11 March 2017

Ana Alegre1,2, Arnaud Bertrand2, Marco Espino1, Pepe Espinoza1,2, Teobaldo Dioses1, Miguel Ñiquen1, Iván Navarro1, Monique Simier2, Frédéric Ménard2 1Instituto del Mar del Perú, Esquina Gamarra y General Valle s/n, Chucuito–Callao. 2IRD, UMR-MARBEC/IFREMER/IRD/UM, Av. Jean Monnet, BP 171, 34203 Sète, France.

ICES/PICES, Symposium on Drivers of dynamics of small pelagic fish resources

Diet diversity of jack and chub mackerels and ecosystem changes in the Northern

Humboldt Current System: a long-term study

diet diversity of jack and chub mackerels and ecosystem ... · la niña 2007 la niña . 1975-76 ....

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