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Forage Fish Food Webs

Margot Hessing-Lewis
Hakai Science
Brian Hunt
University of British Columbia
Hakai Research Associate, Biological Oceanographer
Evgeny Pakhomov
University of British Columbia
Professor
Dan Okamoto
Hakai Postdoctoral Fellow
Resource and Environmental Management (REM)
Program Summary

Forage fish comprise the diverse group of low-trophic level fish species that play a crucial role in marine food webs. They act as intermediaries between plankton and other secondary producers, and shunt energy to top predators such as marine mammals, seabirds and a wide range of commercially important fish species. On the Central Coast of British Columbia forage fish include species such as Pacific herring, sandlance, eulachon, Pacific sardine/pilchard, northern anchovy, and salmon smolt.

Despite their importance to marine food webs, forage fish have by and large remained under researched, leaving substantial gaps in our understanding of their life history parameters, population cycles, and their response to environmental forcing, e.g., ocean warming, and other anthropogenic pressures including fisheries harvests. Filling these knowledge gaps is central to the quantitative parameterization of their ecosystem role, and the development of an ecosystem-based approach to their management.

Through the Hakai Forage Fish Program, our research seeks to understand the following components of the regionally important forage species on the Central Coast:

  1. Life cycle and habitat interactions
  2. Population dynamics – abundance, biomass and size structure
  3. Spatial distribution
  4. Feeding biology (stable isotopes and stomach content analysis)

Through long term monitoring of these parameters, together with complimentary measurements of their prey and predator’s abundance, we aim to understand forage fish population fluctuations and their ecosystem consequences.

Forage Fish Population Biology

Pacific Herring: We monitor herring abundance and distribution at four important life stages: egg (roe), larvae, juveniles and adults.  Herring roe are quantified using dive surveys, and their development on algal substrate is monitored. We quantify larvae, and their emergence from eggs using plankton sampling. Juveniles will be quantified with trawl/seine net surveys, and adults will be quantified using seine surveys. We will also use genetics to understand the spatial structure and connectivity of populations. We are interested in substrate characteristics that influence herring spawning events. For this reason, we collect substrate information in tandem with our dive surveys. We also collect a suite of water column physicochemical characteristics to determine the key triggers for spawning events and larval hatch out.

Sandlance: The pelagic larvae are sampled by plankton net tows, and the post-larval pelagic phase will be sampled by trawl /seine nets. We are using beach seines to quantify benthic phase sandlance abundance in nearshore sandy habitats. We aim to develop protocols to identify key spawning areas, quantify their spawning activity. We are interested in annual changes in beach geomorphology and sediment composition and how this affects utilization of sandy shores by sandlance.

Salmon Smolts: Our focal area of interest is Rivers Inlet, the largest salmon system in the region, historically supporting the third largest sockeye salmon run in British Columbia. Through a number of programs, the salmon smolt in this system have been monitored for a decade. We aim to continue this monitoring work, focusing on the feeding biology of salmon smolt and other pelagic forage fish species, particularly sandlance, herring, and stickleback, and interannual variations in growth rates and competition related to plankton productivity and phenology. In addition to Rivers Inlet research we aim to develop a sister monitoring at Koeye.

Nearshore Fish Sampling

We are establishing a beach seine monitoring program, focused on sandlance, but also quantifying distribution, size structure, and foraging interactions of associated low-trophic level fish such as juvenile salmonid, perch and smelt. Key beaches to be monitored will be located around Calvert island, and in the Koeye River estuary.

Habitat interactions are especially important to forage fish as they provide substrate for spawning events, nursery areas and protection from predators.  While these habitat functions are well known, they are often unquantified. To this end, we will be studying habitat associations of finfish, including forage fish, in seagrass and kelp forest systems in conjunction with the Outer Shores research program.

Pelagic Fish Sampling

We will be using trawl and seine surveys to quantifying juvenile and adult forage fish abundance and seasonal distribution in focal sampling sites, including Kwakshua Channel, Fitz Hugh Sound and River’s Inlet. We will sample forage fish, as well as bycatch from this sampling, to understand their role in local food webs.