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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
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 – Night situation 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
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
Diet diversity of jack and chub mackerels and ecosystems changes in NHCS
Ana Alegre Norza Sior
PICES-ICES 07/03/2017
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
Diet diversity of jack and chub mackerels and ecosystems changes in NHCS
Ana Alegre Norza Sior
PICES-ICES 07/03/2017
We investigate the spatiotemporal patterns of Jack mackerel Trachurus murphyi and chub mackerel Scomber japonicus diet composition.
Objective 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
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
Diet diversity of jack and chub mackerels and ecosystems changes in NHCS
Ana Alegre Norza Sior
PICES-ICES 07/03/2017
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
Diet diversity of jack and chub mackerels and ecosystems changes in NHCS
Ana Alegre Norza Sior
PICES-ICES 07/03/2017
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
Diet diversity of jack and chub mackerels and ecosystems changes in NHCS
Ana Alegre Norza Sior
PICES-ICES 07/03/2017
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
Diet diversity of jack and chub mackerels and ecosystems changes in NHCS
Ana Alegre Norza Sior
PICES-ICES 07/03/2017
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
Diet diversity of jack and chub mackerels and ecosystems changes in NHCS
Ana Alegre Norza Sior
PICES-ICES 07/03/2017
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
Diet diversity of jack and chub mackerels and ecosystems changes in NHCS
Ana Alegre Norza Sior
PICES-ICES 07/03/2017
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
Diet diversity of jack and chub mackerels and ecosystems changes in NHCS
Ana Alegre Norza Sior
PICES-ICES 07/03/2017
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)
Diet diversity of jack and chub mackerels and ecosystems changes in NHCS
Ana Alegre Norza Sior
PICES-ICES 07/03/2017
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
Diet diversity of jack and chub mackerels and ecosystems changes in NHCS
Ana Alegre Norza Sior
PICES-ICES 07/03/2017
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
Diet diversity of jack and chub mackerels and ecosystems changes in NHCS
Ana Alegre Norza Sior
PICES-ICES 07/03/2017
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?
Diet diversity of jack and chub mackerels and ecosystems changes in NHCS
Ana Alegre Norza Sior
PICES-ICES 07/03/2017
• 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?
Diet diversity of jack and chub mackerels and ecosystems changes in NHCS
Ana Alegre Norza Sior
PICES-ICES 07/03/2017
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