Life Beyond the Spawning Grounds: Distribution & Food Web Relations of Herring & Forage Fishes in Puget Sound

Transcription

1 Life Beyond the Spawning Grounds: Distribution & Food Web Relations of Herring & Forage Fishes in Puget Sound Dave Beauchamp, USGS & UW-SAFS Liz Duffy, UW-SAFS (NRDC) Iris Kemp, UW-SAFS Collaborators: DFO-Canada: Dick Beamish, Rusty Sweeting, Chrys Neville Funding: HSRG, Pac. Salmon Commission

2 Most Forage Fish Data Currently derived from Spawning Surveys Trends in spawner biomass, ~age structure, growth & survival estimates by stock & geographic region (e.g., Stick & Lindquist 2009) Less information available regarding ontogeny, seasonal diet, distribution, trophic interactions Environmental & ecological factors affecting survival & growth: Predation Competition Food supply Climate forcing? Water quality? Contaminants?

3 Exploit Similar Info-Needs for Juv. Salmon & Forage Fishes Most life stages can be sampled with the same gear at the same times & locations during the growing season Methodically record data & archive samples of non-target species (freeze) Break down salmon v forage fish silos in research, monitoring & restoration Benefit from economies of scale

4 Objectives Summarize some data collected opportunistically (2001-present): Epi-pelagic distribution & Relative abundance Diet, diet overlap, competition, predation Highlight opportunities for joint R&M efforts to address juv. salmon survival & forage fish questions: Temporal-spatial distribution Food web interactions Stage-specific growth & survival

5 Data Sources DFO-Canada Midwater Trawling July & Sept. cruises ~ Depth-stratified samples in N & C basins: 0-15m, 15-30m, 30-45m, m Future Cruises are highly uncertain beyond Sept NPS CPS ** -Beach Seining N, C, S basins, Apr-Sept -Pilot Purse seining ** June 2003 Mukilteo-Clinton SPS

6 Herring: Nearshore-Offshore Size Structure Fl Bins (mm) Ontogenetic & Seasonal shifts In near-offshore Habitat use & Size structure Proportion 0.4 Nearshore 2001 July 2001 Sep Nearshore 2002 July 2002 Sep OFFSHORE CHINOOK LENGTHS August Sept May-July July Sept

7 Offshore Catch Proportions 1.00 Summer 35,365 8 tows 5, tows July 67, tows 28, tows 17, tows 4, tows Herring catches represent a volatile underestimate of spp composition due to patchy encounters with schools during Daylight tows Forage fish abundance trends from these data are dubious BUT Proportion of Catch Depth distribution patterns useful Excellent source of biological data! Fall 15, tows Coho Herring Chinook Herring Pink Chum 6, tows Sept 3, tows Chinook Pink 35, tows 4, tows 2, tows Chum Pink Chinook Coho Herring Other Relative abundance & distribution Data for juv. salmon considered More reliable than for herring 5 0 Chum

8 Split-beam Hydroacoustics Targets mm Depth (m) July August September Density (Targets/1000m )

9 Abundance & Spatial-Temporal Overlap of Potential Pelagic Competitors Daylight Planktivore Community Herring dominated the Biomass of epi-pelagic Planktivores during Critical July growth period 15 Mean Catch/hr All planktivorous fishes Concentrated in 0-15m During July. Depth (m) 30 Chinook Other Salmon (30% pink salmon) Herring Other Spp July 2004 DFO Ricker Midwater trawl

10 Purse Seining: Live Capture of Pelagic Salmon

11 Epi-Pelagic Fish Community Sampled with Purse seines Juvenile salmon & forage fish Prevalent in epi-pelagic zone Catch per Haul June Daylight purse seining Purse seine, June 2003 Whidbey-Mukilteo W Chinook H Chinook Coho Chum Dusk Forage fish abundance MUCH HIGHER than juv salmon Surf Smelt & Herring dominate The epi-pelagic catch Surf smelt densities seem higher Closer to shore slope than in mid-channel Smelt rare in Ricker MW Trawls Catch per Haul W Chinook H Chinook Coho Chum Herring Smelt West Bottom Depth (m) East Dusk

12 DAYLIGHT: Mukilteo (7:38pm) to Possession (7:57pm) 60 m

13 DUSK: Whidbey by Clinton Ferry 9:36-9:45pm 60 m

14 Summer Herring Diet by Size class, Year, and Month Volumetric proportion PS Offshore Herring Diets (<130 mm) July n = mm n = 4 92 mm PS Offshore Herring Diets (>130 mm) JULY n = mm n = mm n = mm n = mm COPEPOD CRAB LARVAE EUPHAUSIID GAMMARID HYPERIID OSTRACOD CHAETOGNATH LARVACEAN INSECT OTHER Volumetric proportion Sep COPEPOD CRAB LARVAE EUPHAUSIID GAMMARID HYPERIID OSTRACOD CHAETOGNATH LARVACEAN INSECT OTHER n = mm SEP n = mm n = mm n = mm n = mm Small herring feed more heavily on Copepods than older herring Larger herring eat more crab larvae & amphipods

15 Winter Herring Diet by Size class, Year, and Month 1.2 PS Winter Offshore Herring Diets <130 mm 1.0 n = mm COPEPOD CRAB LARVAE EUPHAUSIID GAMMARID HYPERIID OSTRACOD CHAETOGNATH LARVACEAN INSECT OTHER >130 Mar mm 2008 Feb 2010 n = mm n = mm Mar 2008 Feb 2010 Small herring feed more heavily on Copepods than older herring Larger herring eat more amphipods

16 Strong Diet Overlap during Critical Growth Period Between juvenile Salmon spp. and Herring Key Prey Overlap: Crab Larvae Hyperiids Euphausiids JULY Key Prey & degree of Diet overlap Vary among years Chum Salmon show Least overlap with Other salmon & herring n = mm Chum n = mm n = mm n = mm Chum Pink Herring Chinook Coho n = mm n = mm n = mm n = mm n = mm n = mm Pink Herring Chinook Coho Insect Gammarid Hyperiid Crab Larvae Copepod Euphausiid

17 Herring Size-at-Age (from Stick & Lindquist 2009) 100 Body Mass (g) SPS CPS NPS Age

18 Potential Inter-specific Competition for Food Herring remove 10-47x more Biomass of key shared prey than H+W Chinook during Critical May-July period CONCLUSION: On average, Competition driven 1 o by Herring in pelagic Habitats of Puget Sound. Prey consumption demand (MT/season) But-Competition should be Considered across the entire Epi-pelagic planktivore community x Copepod Crab Larvae Population-level consumption demand 2008: SPS, CPS, NPS 10x 45x Euphausiid Gammarid by Herring age 0-4 by Chinook age-0 47x Hyperiid Other Intensity of competition will likely Vary among regions & months, based on relative abundance & diet of each species

19 Exis%ng Knowledge Epi- Pelagic plank/vore community biomass dominated by herring Significant diet overlap between Herring and Juvenile Chinook Herring consume 10-40x the biomass of prey shared by Chinook Poten/al for considerable compe//on effects on growth Other salmon and forage fishes also overlap and compete, but impose lower consump/on demand than herring

20 Conclusions & Recommenda/ons Consider Carrying Capacity for en/re plank/vorous fish community rather than for single species Considerable diet overlap among Herring & juvenile salmon. Less know about other forage fishes Forage fish biomass & dynamics can poten/ally overwhelm trophic effects of juv. salmon Must consider interac/ons at proper temporal- spa/al scales Compe//on could vary significantly among regions, months, & years Need zooplankton data!!

21 Predators

22 Sea-run Cutthroat Trout Spring-Summer Diet by size class mm Cutthroat trout Relatively low abundance Primarily a nearshore predator Smaller Less Piscivorous trout Eat juv. salmon & sandlance Larger (FL > 250 mm) trout are Highly piscivorous and primarily eat Herring & juv Salmon Diet Proportion by Wt Diet Proportion by Wt May Junemm Cutthroat July Aug trout Sept Invert Salmon Chum Chinook Coho Sandlance Herring OthFish May June July Aug Sept

23 Predatory Juvenile & Resident Chinook Salmon Relatively abundant predator Feed in Nearshore & Offshore Habitats Nearshore predation by juveniles primarily in June-July Offshore predation year-round by Resident & older juvenile Chinook

24 Frequency Size-selective Predation Puget Sound Chinook in midwater trawls Prey Size : Predator Size Nearshore % 50% Predator L Chinook Chum Pink Salmon Sand lance Herring Bay pipefish Perch Stickleback Fish Sample Proportion Piscivore Size Distribution Fork length (mm) Size-selective cannibalism: Sizes of age-0 Chinook eaten vs available Offshore in July Fork length (mm) Eaten Available Prey fish FL (mm) Offshore 50% % Predator L Chinook FL (mm)

25 Size-selective predation on Herring by Juvenile & Resident Chinook Salmon Sample Proportion A B Age-0 Chinook prey Herring in trawl 0 Age 1-3 Chinook prey Herring in trawl Fork length (mm) Herring found in age-0 Chinook stomachs are significantly smaller than those sampled Concurrently with MW Trawl Same for larger resident Chinook

26 Size-selective predation by Chinook on Sand Lance is less evident Sample Proportion A B Sand lance Age-0 Chinook prey Sand lance in trawl Age 1-3 Chinook prey Sand lance in trawl Fork length (mm)

27 Simulated Predation Demand by Resident Chinook in Puget Sound FL > 300 mm Population Consumption (MT) Chinook Pink & Chum Herring Sand Lance Other Fish Inverts May June July Aug Sep Oct Fall Win Apr Month - Season -Herring are the predominant prey of Chinook >300 mm throughout the year -Over 1,500 metric tons of herring consumed by resident Chinook annually in PS

28 Other predators Harbor Porpoise & Harbor Seal populations have increased significantly over recent decades Piscivorous birds? Demersal fishes?

29 Exploit Similar Needs for Ecology of Juv. Salmon & Forage Fishes Much to be learned about how food web processes & environmental factors limit forage fish: Seasonal food supply & demand Competition Predation mortality, Disease Most life stages can be sampled with the same gear Ichthyoplankton sampling an important exception Methodically record data & archive samples of non-target species (freeze) Break down salmon v forage fish silos in research, monitoring & restoration Benefit from economies of scale