The role of squid in linking marine ecosystems Alexander I. ARKHIPKIN

Transcription

1 The role of squid in linking marine ecosystems Alexander I. ARKHIPKIN Fisheries Department Falkland Islands Government Stanley FALKLAND ISLANDS

2 Highly migratory fish Pacific salmons Open ocean coastal waters and rivers

3 Highly migratory fish Norwegian spring-spawned herring Open ocean shelf and coastal waters The biomass transported to the coast and left as reproductive output (eggs) is about 1.3 mln tonnes for the current population. Source: Ø. Varpe, Ø. Fiksen and A. Slotte (2005)

4 Highly migratory squid Nektonic ommastrephids (Illex illecebrosus) Opposite direction: From shelf and coastal waters to the open ocean Source: Hatanaka et al. (1985)

5 Illex argentinus as a model species of nektonic squid Many aspects of its biology and ecology are well-studied. It inhabits shelf, slope and open pelagic waters of the Southwest Atlantic It has a 1-yr life cycle Intra-specific groups of Illex argentinus Spring-spawning group Summer-spawning group Autumn-spawning group Winter-spawning group (WSG) - the most abundant, and has the longest ontogenetic migrations

6 Migrations of the winter-spawning group of Illex argentinus Hatching: August Pelagic larvae and juveniles: Sept-Nov 200m Start of shelf migration: Dec Age: 160 d, ML=12-13 cm Shelf life: Jan-Apr Falkland Current Start of slope migration: May Age: 280 d, ML=28 cm Slope migrations: June-July

7 Main aims of the study 200m INPUT: What biomass of squid moves onto the shelf at the start of migrations INTEREST RATE and EXPENDITURE: Biomass production on the shelf OUTPUT: What biomass of squid goes out of the shelf to slope

8 Means: Excel spreadsheet P/B Coeff Growth F Growth M Growth F DGR BW RDGR Total gain, g Growth M ML ML BW F F F BW DGR BW RDGR Total gain, g Growth M alive Age Constant Step dead Females Males Females Females Females BW E E E E E E E E E E E E

9 Assumptions Equilibrium population Population size does not change through time Population size is at equilibrium when amount of births and immigration balance death and emigration In case of the winter-spawning Illex argentinus Total amount of eggs produced by a single female (realized fecundity) and spawned should produce two adult squid (male and female) by the next spawning 1 year life cycle (10 d of egg development d of post-embryonic life) Average realized fecundity = 400,000 eggs (Laptikhovsky, Nigmatllin, 1992) Egg mortality is negligible (Sakurai et al., 1996)

10 Growth curve Mantle length, cm Females Males Age, d Asymptotic growth described by the Shnute s growth curve for both sexes (Arkhipkin and Roa, 2005).

11 Daily growth rates, g/day Females Males Individual growth rates Age, d Individual absolute growth rates (DGR) are maximum at age of d RDGR in weight Females Males Individual relative growth rates (RDGR) are maximum in early larvae Age, d

12 Cohort numbers and mortality Numbers Constant Step Age, d 1. Constant daily mortality rate: Step daily mortality rate: as in gadoid larvae at C (0.192, Houde and Zastrow, 1993)) for the first 40 d (duration of larval phase, Arkhipkin, 1990), and then until the end of ontogenesis.

13 Cohort numbers and mortality

14 Total biomass of the cohort Biomass, g Total Females Males Age, d Maximum cohort biomass (B cj = N cj W ij ) is observed on the shelf at age of 240 d

15 Total biomass of the cohort Maximum cohort biomass (B cj = N cj W ij ) is observed on the shelf at age of 240 d

16 Total cohort biomass in teleost fish and cephalopods

17 Cohort absolute daily gain and loss (in weight) Population daily gain, g/d Females Males 50 Total Age, d Cohort daily growth rates are maximum at age of 190 d (DGR cj = N cj DGR ij ) 70 Population daily loss, g/d Females Males Total Cohort daily loss rates are maximum at age of 240 d (LR cj = N Lj W ij ), where N Lj = N cj N c(j-1) Age, d

18 Cohort absolute daily gain and loss (in weight) Cohort daily growth rates are maximum at age of 190 d (DGR cj = N cj DGR ij ) Cohort daily loss rates are maximum at age of 240 d (LR cj = N Lj W ij ), where N Lj = N cj N c(j-1)

19 Cohort daily rations Feeding spectrum of Illex argentinus in the Patagonic region per size category (Brunetti et al., 1998) Population daily rations, g/d 250 Total ration 200 Amphipods Euphausiids 150 Fish 100 Squid Age, d Cohort daily rations, assuming gross conversion efficiency of 29% (Hirtle et al., 1981)

20 Account statement of the cohort Shelf Slope Total Age at start at finish Number at start ,000 at finish Biomass (g) at start 1,667 2, at finish 2,627 1,492 1,492 Total gain (g) 5,791 1,057 9,478 Total rations (g) 19,969 3,640 32,684 Total loss (g) 4,890 2,208 8,233 P/B coefficient 6.5

21 Account statement of the cohort Shelf, d Slope, d Weight, kg Biomass (start) Biomass (finish) Total gain Rations Total loss

22 Account statement of the whole winter-spawning group Data from the r/v Shinkai Maru survey in Jan-Mar 1979 (Sato, Hatanaka, 1983) Shelf Slope Total Age at start at finish Number at start 1.23E E E+14 at finish 2.06E E E+08 Biomass (thousand t) at start at finish Total gain (thousand t) 1, ,247 Total rations (thousand t) 6,841 1,247 11,197 Total loss (thousand t) 1, ,821

23 The unique life history traits of abundant nektonic squid, such as Illex argentinus, suggest that squid may function as fast-acting biological pumps, conveying substantial biological production between different oceanic ecosystems. Life history traits Long-distance migrations Semelparity Relatively low mortality on the feeding grounds High food conversion rates One-way transfer of biomass from the feeding grounds to spawning grounds

24 Types of squid ecosystem linkages Illex argentinus pump

25 Types of squid ecosystem linkages Loligo gahi pump

26 Types of squid ecosystem linkages Dosidicus gigas pump

27 Types of squid ecosystem linkages Onychoteuthis banksi pump

28 Large-scale biomass transport between marine ecosystems by nektonic squid is vulnerable to increasing environmental variability

29 Illex argentinus Annual catch Temp. anomaly Annual catch, t temperature anomaly Year Work of Claire Waluda, Phil Trathan, Paul Rodhouse (BAS) Catch (tonnes) per vessel of Illex argentinus in Falkland Islands waters ( ) versus SST in the norhern Patagonian Shelf in July prior to the fishery starting next February. Regression line and 95% confidence intervals (R 2 =0.413).

30 Illex argentinus common year on the Patagonian Shelf

31 Illex argentinus cold year on the Patagonian Shelf

32 Illex illecebrosus мнт Petawatts 1950s Schematics of the latitudinally averaged volume transport (in Sverdrups) The estimates are presented for three time slices and four layers upper (red), intermediate (green), deep (blue) and bottom (yellow). мнт 1980s мнт s Annual catch, t Annual catch Temp. anomaly temperature anomaly Year

33 Todarodes pacificus Annual catch, t Annual catch Temp. anomaly temperature anomaly Year Schematic summary of interannual variability in the extension of the inferred spawning areas during February,

34 Dosidicus gigas Annual catch, t Annual catch Temp. anomaly temperature anomaly Year Small group ( mm ML) Medium-sized group ( mm ML) Large group ( mm ML) (according to Nigmatullin et al., 2001)

35 Conclusions Our data show that nektonic squid can act as biological pumps and make important contributions to the exchange of resources between ecosystems. These pumps are sensitive to small changes in the environment and fishing induced mortality. Nektonic squid populations are highly sensitive to environmental variability and it is predicted that variability will increase as a consequence of global climate change. Changes in the environment due to the global climate change and unregulated fishing effort could therefore have long-term consequences for ecosystem structure where these pumps occur.