Elisabeth Duffy*, David Beauchamp
Juvenile salmon are moving through Puget Sound (PS) from April-July. By end of July most have made it to the deep ocean. Percent of fish from hatcheries is about 50% in N PS and 90% in S PS.
Nearshore fish comunity: herring and perch up north, hatchery salmon dominate in the south; salmon are 30-130mm, herring 130-160cm, sand lance 100-130cm; north diets dominated by insects, south diet by crab larvae, euphausids; predators drive early mortality and salmonids dominate (cutthroat target smallest juveniles)
Overall, marine survival has been really low, and lowest during pink years. The bigger the fish are in July, the better their marine survival.
Where do we go from here?
- synthesize data across Salish Sea
- Prey supply (zooplankton) is a big data gap
Theresa Liedtke et al focuesd on 2 forage fish species: Pacific sand lance and Pacific herring
Initially focused on Liberty Bay (Poulsbo, WA; today’s data) with non/urban coastline; now working at Possession Point (s Whidbey Island) to get higher wave action and feeder bluffs. 12 sand/sediment samples, 500ml samples preserved eggs.
Findings: 40k eggs in Liberty Bay, 83 per sample; predominantly surf smelt (94%), sandlance and rock sole remaining; >60 eggs/sample called “high egg count” sample and included in a regression.
High egg counts associated with: shell fragments, high position on beach, and proximity to sediment source (eggs moved by wave action?). If you had all 3, you had 82x chance of finding eggs on that beach. Not associated: armoring, shade, freshwater input, upslope development.
Thus far, no eggs at Possession Point.
Data from N end of Bainbridge and repeat trawl survey from Tom Quinn’s UW class (~20 trawls/year from 1991-2008, over 2nd weeend in May, 4 depths (10-70m)). Time series started just after 1989 fish closure, so expected increase in catch rate over time, but that wasn’t the case.
Catch anomaly shows an actual catch that is higher than expected (based on number of trawls completed compared with historical average for that depth and location). Catch anomaly decreases for rockfish and slendersole, but increased for english sole. Some species show up episodially: 1990 pulses of shiner perch, mid90s pulse for Pacific hake, big tomcod pulse in 2000, and 2003-4 for walleye pollock. No trend in ratfish. English sole was most abundant overall.
It’s unclear why these declines have occurred. WDFW has sometimes seen increases for the same species and years in other parts of Puget Sound.
Vancouver Aquarium Marine Science Center
Focusing on quillback rockfish and interactions with one of their prey, 3 genera of demersal shrimp which show strong spatial association. An example from 8 reefs in Howe Sound and adjacent Georgia Strait, depths 14-25m, daytime, 10 Jul – 18 Nov, 2008
Lingcod are the main predator of quillback rockfish. Estimated biomass in Strait of Georgia down 90% in last 100 years, majority in Howe Sound are <75cm. Smallest quillback should have strongest avoidance of encounters with lingcod at the expense of access to the shrimp. Counts per minute (CPM) of small quillbacks rise with shrimp and fall with lingcod. Large quillback CPM also rises with shrimp, but doesn’t alter with rising lingcod.
If we control for structural complexity of the habitat, then shrimp CPM decreases with rising activity of rockfish.
Predators should be managed not for demographic persistence alone, but for the maintenance of risk-driven ecological processes.
What are the interacting relationships between rockfish, the lingcod that eat them, and the fishers who take lingcod (and rockfish)? In reserves we can look at predatory role of lingcod without fishing pressure. We can also look at differences in lingcod population structure and feeding between non/reserves.
Most samples from central San Juan Channel in rocky habitat.
- non-reserve: 35-80cm, mean ~45cm
- reserve: quite a few large females, 80-120cm.
Catch rate: in reserves we had many more days when we caught >3 lingcod/hour.
Acoustic telemetry synopsis
- Limited movement: 8/9 tagged lingcod never left reserve
- Diet composition: rock fish are 20% of diet in reserves, only 5% in non-reserves (maybe because there are more rockfish in reserves, or maybe larger rockfish in reserves eat more rockfish, or maybe there are habitat differences)
- Estimated rockfish consumption (modeled): consumption of rockfish in reserves may have been 5x non-reserve, with implications for how to recover rockfish!
- Pop structure differs between non/reserves
- diet variations suggest local diffs in fish communities
- there are unexpected ecological consequences of creating reserves…
- match scales of research and management (got to get down to pretty small scales!)