Marrowstone Marine Field Station
Puget Sound Forage Fish
In Washington State, “forage fish” refers to a collective assemblage of pelagic species including Pacific herring, Pacific sandlance, surf smelt, northern anchovy, pricklebacks, etc. (in unknown order of relative biomass or ecological importance). Aside from limited information regarding populations size and age structure of Pacific herring in Puget Sound, major information gaps exist in basic knowledge of forage fish stock abundances, assemblages, and roles in healthy ecosystem function. Basic information necessary to responsibly manage forage fish populations, including gross population sizes, relative abundances, bioenergetic values, and environmental / anthropogenic factors affecting abundances and demographics is not available.
Of all forage species in Puget Sound, the vast majority of scientific monitoring and research effort is currently directed towards Pacific herring, likely because global, commercial markets exist for herring and herring products. Therefore, the majority of herring effort has been directed towards generating biomass numbers and population trends that are pertinent for fishery management purposes.
In addition to their commercial value, Pacific herring are ecologically important and integral at all trophic levels of the food web. The estimated carbon contribution of herring spawning products to the Strait of Georgia (including northern Puget Sound) during the spring spawning period is greater than maximum estimates of primary productivity during the same period. Herring eggs and larvae are used as a primary food source for invertebrates including crabs, medusae, ctenophores, chaetognaths, and amphipods; fish including juvenile salmonids, sturgeon, smelt, and surfperches; and marine gulls and diving birds. Juvenile and adult herring serve as the primary prey for marine mammals including harbor seals, sea lions, and endangered orcas and finfishes including endangered Chinook salmon, coho salmon, Pacific cod, Pacific hake, lingcod, and halibut. As a result of the current single-species management approach employed to Pacific herring studies, major information gaps exist in herring biology / ecology that impede effective ecosystem management. For example, aside from the approximate 4 week period in late winter when adult herring return to known spawning areas throughout Puget Sound, their whereabouts, including migration and residency patterns, remain unknown. Additionally, ecological and anthropogenic factors influencing herring population abundances and demographics remain largely unknown and understudied.
The ability to accurately predict future herring population trends and assess their impacts to organisms at other trophic levels via wasp waist control will remain intangible until basic studies are conducted to understand the role of herring in the Puget Sound ecosystem; this approach must extend beyond the traditional single species management approach that currently exists.
For forage fish species with little or no perceived commercial value like Pacific sandlance, surf smelt, northern anchovy, etc., assessment and research efforts have historically been nonexistent and / or under-funded even though their biomasses and ecological significances likely exceed those of Pacific herring. For example, on average, 35% of the diets of juvenile salmon (60% of the diet of juvenile Chinook salmon) in Puget Sound are comprised of sand lance. Intertidal spawning habits of sand lance and surf smelt predispose them to negative effects of shoreline development; in Puget Sound >200 miles of shoreline are utilized as spawning beaches for surf smelt and >140 miles of shoreline are utilized as spawning beaches for sand lance. Aside from a recent WDFW-led, effort to inventory beaches utilized as spawning habitat by sand lance and surf smelt, no current or past stock assessment or monitoring has been conducted. Additionally, anchovies were likely once a predominant forage species in Puget Sound:
“The anchovy come to Puget Sound in enormous quantities, and…every bay and inlet is crowded with them…I have known them to be in such masses at Port Hadlock that they could be dipped up with a common water bucket.”
- Anonymous, 1894
Anchovy biomass in Puget Sound is currently well below these historic levels, but anecdotal observations in south Puget Sound indicate that biomass has been increasing dramatically in recent years. Unfortunately, the gross and relative abundances of these forage fish species remain unknown and environmental and anthropogenic factors influencing their abundances and demographics remain largely uninvestigated.
In Puget Sound abundances and demographics of Pacific herring populations have changed dramatically in recent years. Biomass of herring at Cherry Point, historically the largest of the 18 herring populations in Puget Sound, has decreased from nearly 15,000 mt in the early 1970's to 1,126 mt in 2001. Additionally, the mean estimated annual mortality for Pacific herring in Puget Sound (exclusive of commercial fishing) has increased from 20-40% in the late 1970’s and early 1980’s to 64-87% in recent years. Throughout this period the median age of iteroparous herring has decreased from 5+ yr cohorts to 2-3 yr (newly recruited) cohorts that fail to return the following year. We hypothesize that these population trends are the result of parasitic disease-related mortality, particularly among under-represented, older cohorts. Ichthyophonus hoferi, a protistan parasite historically associated with episodic mortalities to populations of Atlantic herring is currently ubiquitous among many herring populations on the west coast of North America. In Puget Sound prevalence of I. hoferi increases directly with herring age from 12% among 0yr cohorts to 58% among the under-represented, 6+ yr cohorts. Further, I. hoferi is highly pathogenic to immunologically naïve Pacific herring, causing 80% mortality 2 mo. after injection challenge. Considering that infections of I. hoferi among less than 10% of plaice captured near Scotland were estimated to result in annual mortalities of over 50%, we hypothesize that the infection levels detected among herring in Puget Sound can conservatively account for their recent high natural mortality rates.