Fishery interaction and availability of Atka prey for Steller Sea lions: Results from local abundance and movement study of Atka mackerel

S. F. McDermott1, E.A. Logerwell,1 I. Ortiz,2 and V. Haist1 1Alaska Fisheries Science Center 2 Northwest Fisheries Science Center National Marine Fisheries Service Overview

• Background • Research goal • Atka mackerel tagging study • Small Scale Food web model (Libby Logerwell) • Conclusions Background information

• Atka mackerel ( monopterygius) is one of the most abundant groundfish in the Aleutian Island area (2004 Biomass ~ 336, 345mt, 2003 Fishery landings ~58,585 mt) • Important component in the ecosystem – Prey: Euphasiids, , Myctophids – Predators: Steller Sea lions, P. Cod, Halibut, Arrowtooth fl. • Patchy distribution on large and small scales Atka mackerel and where Steller Sea lions

¿ Western stock of was declared endangered in 1997 ¿ Trawl exclusion zones established around rookeries, haulouts ¿ Atka mackerel prevalent in diet (78% occurrence in the Aleutians) Research goal

• Study efficacy of trawl exclusion zones (TEZs) in preserving prey abundance for Steller Sea lions – Estimate local abundance and movement in and out of the TEZs – Small-scale food web model Tagging as means of abundance estimation

– Local abundance and localized movement can be estimated (patchiness not as problematic as in other survey methods) – Tag recovery pays partly for research effort – Fishery can be used in tag recovery (cost-effective) • Assumptions: – Population is closed within study area (no immigration or emigration) – Tagged fish mix randomly with untagged fish – All fish have same recovery probability – Tag shedding, tag mortality, tag reporting rates can be estimated with auxiliary data Project History

2006 2002 2003 2000 2002 1999 (Pilot)

Kiska Island

Amchitka Island Tanaga Pass Seguam Pass Tagged fish release locations Methods

• 1999-2006 • released over 75,000 tagged fish • 2006 tag release and recovery effort cooperative funding with industry

• Model – Integrated tagging model using maximum likelihood (Hilborn 1990) – Estimates • N (population size) • p (probability of moving) • Tag mortality • Tag reporting rate •Tag loss Catch… Tag… Release… Recapture Recapture Abundance estimates

600

Inside TEZ 500 Outside TEZ R In-and Outside TEZ 400 E -D 300 O

200 Number of fish (millions) Number of fish 100

0 Seguam Tanaga E Tanaga W Amchitka Amchitka Kiska (2002) (2002) (2002) S (2003) N (2003) (2006) Area Movement rate

0.05 inside to outside

0.04 outside to inside 0.04 R 0.03 E -D 0.03 O 0.02

0.02

0.01

0.01

0.00 Seguam Tanaga E Tanaga W Amchitka Amchitka Kiska (2002) (2002) (2002) S (2003) N (2003) (2006) Area Biomass in all areas combined

400

350

300

250

200

150

100 Biomass (Thousands of mt) Biomass (Thousands 50

0 Biomass Inside TEZ Biomass Outside TEZ Stock assessment (2004) Small-scale food web model

• Is there enough Atka mackerel production inside Trawl Exclusion Zones (TEZs) to support Steller sea lions? • Construct a food web model for each TEZ Small-scale food web model

Fish predators: Steller sea lions Pollock Halibut Skates

Atka mackerel Production Small-scale food web model Data • Atka mackerel – Biomass from tag model – Production rate (P/B) from Aleutian EcoPath model • Steller sea lions – Biomass from derived counts, age-structure, sex ratio, pregnancy rate, and weight-at-age – Diet from scat collections – Consumption rate (Q/B) from Aleutian EcoPath model • Fish predators – Biomass from trawl survey – Diet from trawl survey collections – Consumption rate (Q/B) from Aleutian EcoPath model Results – Seguam Pass 2002

Tagged Atka mackerel release locations Results – Seguam Pass 2002

Trawl survey strata

•Biomass for fish predators, by strata Results – Seguam Pass 2002

Trawl survey strata in 3-degree area

•Biomass for fish predators from strata biomass weighed by CPUE •Diets for fish predators Results – Seguam Pass 2002

Trawl Exclusion Zone (TEZ)

•Biomass for fish predators from 3-degree area biomass weighed by area (km2) •Biomass for Atka mackerel from tag model Results – Seguam Pass 2002

Steller sea lion rookeries/haulouts

•Biomass for sea lions from population model •Diet for sea lions from scat collections Data Details Data Year(s) Season(s) Sample size Source

Survey strata biomass 2002 Summer 119 hauls AFSC

3-degree area CPUE 2002 Summer 72 hauls AFSC

Fish predator diets 2000- Summer Pollock 349 stomachs AFSC 2006 Arrowtooth Flounder 391 Halibut 115 Pacific cod 317 Skates, 1997-2006 26 Atka mackerel 2002 Summer 24,999 tagged fish released McDermott biomass 58 tagged fish recovered Steller sea lion 1977, Fay (UW) biomass 2000 Holmes, Fritz (NMML) Steller sea lion diet 1990- Summer 231 scats NMML 1999 (mostly) Results - “current” sea lion population (2002)

Arrowtooth Pacific cod flounder Aleutian Walleye pollock Alaska skate Whiteblotched skate Steller sea lions

Unconsumed

Proportion of Atka mackerel production consumed Results – “recovered” sea lion population (1977)

Arrowtooth Pacific cod flounder Pacific halibut Walleye pollock Alaska skate Whiteblotched skate

Steller sea lions

Unconsumed Proportion of Atka mackerel production consumed Conclusions Efficacy of trawl exclusion zones at mitigating competition between sea lions and commercial fisheries varies geographically •Do fish move from inside to outside? – Small movement at Seguam and Tanaga and Kiska – Large movement at Amchitka •What is the abundance of fish inside? – Large biomass at Seguam, Tanaga, and Kiska – Small biomass at Amchitka – Food web model indicates that there is enough Atka mackerel production for sea lions at Seguam (current and “recovered”) Acknowledgements • Atka mackerel tagging study: – North Pacific Fisheries Foundation – Crew of the Seafisher – Crew of the Pacific Explorer – Kimberly Rand, Dan Cooper, all AFSC scientists collecting data in the field – Cascade Fishing: Phil Dang, Tim Meintz, Nancy Kercheval