How does release density affect enhancement success for hatchery-reared red king crab?

Transcription

1 ASFC How does release density affect enhancement success for hatchery-reared red king crab? W. Christopher Long, Peter A. Cummiskey, J. Eric Munk July 21, 2017

2 AKCRRAB Alaska King Crab Research, Rehabilitation and Biology Gulf of Alaska fishery closed in 80s No recovery since Stock enhancement? Kodiak Area Red King Crab Harvest Millions of Pounds Year Sagalkin, N. H Annual management report for the shellfish fisheries of the Kodiak, Chignik and Alaska Peninsula Areas, Alaska Department of Fish and Game, Fishery Management Report No , Anchorage. U.S. Department of Commerce National Oceanic and Atmospheric Administration NOAA Fisheries Page 2

3 Field release questions How do we maximize release success? Is enhancement ecologically feasible? Is enhancement economically feasible? (Won t get to this one today) What could influence release success? Habitat Density Time of release Size at release Predation Environmental variables U.S. Department of Commerce National Oceanic and Atmospheric Administration NOAA Fisheries Page 3

4 Methods: Site Trident basin ft depth Complex habitat Cobble Shells Macroalgae U.S. Department of Commerce National Oceanic and Atmospheric Administration NOAA Fisheries Page 4

5 Effects of release density: Methods Crabs reared at Alutiiq Pride Shellfish Hatchery Transect 5 x 5m plots Three release densities Three replicates of each Randomized order Crabs counted out for each plot Released on Aug. 4, m 5 m 0 m m m m m U.S. Department of Commerce National Oceanic and Atmospheric Administration NOAA Fisheries Page 5

6 Methods Density 50 x 50 cm quadrat Counts by diver 3 inside, 3 outside plots Habitat and predators noted Predation Once a month Tethering 15 cm tether Tether in late afternoon Check next morning and after 24 h Predator transects for larger mobile ones U.S. Department of Commerce National Oceanic and Atmospheric Administration NOAA Fisheries Page 6

7 Result: Density over time Fit to model with migration (diffusion) and mortality High mortality on the first day Combination of migration and mortality U.S. Department of Commerce National Oceanic and Atmospheric Administration NOAA Fisheries Page 7

8 Results: Emigration Emigration detectable in 3-4 days Substantial portion of crabs lost from plots due to emigration No difference among treatments U.S. Department of Commerce National Oceanic and Atmospheric Administration NOAA Fisheries Page 8

9 Results: Proportion remaining Very low loss during last couple months No difference among treatments Estimated mortality would lead to ~15% survival after a year U.S. Department of Commerce National Oceanic and Atmospheric Administration NOAA Fisheries Page 9

10 Results: Mortality rate Mortality rate decreased with time Reduced by about 90% in the first 2 months No difference among density treatments U.S. Department of Commerce National Oceanic and Atmospheric Administration NOAA Fisheries Page 10

11 Results: Tethering No effect of release density Decrease over time Predator density? Temperature? Crab size? Night/Day Initial vulnerability? Crepuscular predators? U.S. Department of Commerce National Oceanic and Atmospheric Administration NOAA Fisheries Page 11

12 Results: Predators inside quadrats Non-metric Multidimensional Scaling 2D Stress: 0.01 Treatment No difference among treatments Common predators Hermit crabs Shrimp Gunnel Arctic shanny Ronquil U.S. Department of Commerce National Oceanic and Atmospheric Administration NOAA Fisheries Page 12

13 Results: Mobile Predators No difference among treatments No difference among months Common predators Rockfish Ronquil Greenlings Sculpins U.S. Department of Commerce National Oceanic and Atmospheric Administration NOAA Fisheries Page 13

14 Conclusions Part I High mortality right after release, ~65-70% Lower mortality rate afterwards ~85% total mortality over 1 year Substantially, ~3 x, better survival than SE Alaska (Loher et al. 2000) Survival rates are consistent with or better than wild stocks in harvested populations Crabs emigrate Random walk a good fit No density dependence Loher, T., and Armstrong, D. A Effects of habitat complexity and relative larval supply on the establishment of early benthic phase red king crab (Paralithodes camtschaticus Tilesius, 1815) populations in Auke Bay, Alaska. Journal of Experimental Marine Biology and Ecology, 245: U.S. Department of Commerce National Oceanic and Atmospheric Administration NOAA Fisheries Page 14

15 Conclusions Part II Predation decreases throughout the fall Predator abundance does not change Changing temperature or crab size? Densities tested do not affect Mortality rates Emigration rates Predation risk Predator abundance Releases can occur at high densities U.S. Department of Commerce National Oceanic and Atmospheric Administration NOAA Fisheries Page 15

16 Next steps How do we increase initial survival? Netting or predator exclusion cages Release at night Condition crabs Other considerations to maximize success Timing (season) of release Size at release U.S. Department of Commerce National Oceanic and Atmospheric Administration NOAA Fisheries Page 16

17 Thanks! Alutiiq Pride Shellfish Hatchery All AKKCRAB Partners Nikki Gabriel Nick Sisson Ben Daly Kathy Swiney Robert Foy Kodiak Wet Lab Staff U.S. Department of Commerce National Oceanic and Atmospheric Administration NOAA Fisheries Page 17