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Report Series J: Marine Nearshore Fish and Benthic Invertebrates


Oct. 1, 2009

This release, Marine Nearshore Fish and Benthic Inver tebrates, is the tenth in the Pebble Par tnership’s Pre-Permitting
Environmental and Socio-Economic Data Repor t series. Nearshore fish include those found from the high tide line through
the shallower waters of the study area, and includes both demersal (on or near bottom) and pelagic (water column) species.
Benthic inver tebrates are those living near, on, or within bottom sediments.
Since 2004, the Pebble Par tnership has retained independent environmental consultants and laboratories to conduct marine
studies in Iliamna Bay and Iniskin Bay. Data were gathered by Pentec Environmental/Har t-Crowser Inc., Bristol Environmental
and Engineering Services Corporation, University of Alaska Fairbanks (UAF), and RWJ Consulting.
This release includes data per taining to the benthic and nearshore communities of Iliamna Bay and Iniskin Bay. Similar to the
Marine Nearshore Habitat release, the study area includes nearshore marine waters and shorelines from the east entrance of
Iniskin Bay and Scott Island to the south entrance of Iliamna Bay at South Head and encompasses areas under consideration
for a new port site and access road. The objectives of the Marine Nearshore Fish and Benthic Studies are:
• to build upon the considerable knowledge available from past studies to document baseline conditions, including
seasonal, annual and tidal variations, as well as elevation;
• to document the food web and ecological relationships among key species in the areas studied;
• to investigate Pacific herring spawning;
• to identify and map specific habitats and/or resources (e.g., kelp and eelgrass beds, marshes at stream mouths, shellfish
resource areas, etc.)
The information presented here was gathered between 2004-2007 and builds upon
studies that began in the 1970s by the same lead investigators. Field work completed
for the Pebble marine studies included:
• aerial reconnaissance (including mapping and remote sensing)
• inter tidal reconnaissance;
• inter tidal sampling;
• beach seining;
• subtidal reconnaissance (diving);
• subtidal sampling; and
• trawl sampling.
Study Summary
Generally, the inter tidal areas sampled represent a wide range of habitat types from bedrock to mudflat. Each habitat type
suppor ts a distinct mix of resident organisms that have adapted to the physically rigorous environment in Iliamna Bay and
Iniskin Bay. The inter tidal zones’ plant and animal diversity tends to decrease in areas that are protected from wave action
and have relatively high suspended sediments. Ice damage and low light levels combine to greatly reduce inter tidal organisms
each winter, with the effects of moving ice exacerbated by ocean swells. Organisms may overwinter as ice-resistant holdfasts,
Sea anemone (Urticina crassicornis)
and typical cobble/boulder habitat near
North Head.
in crevices or under boulders, or by migrating to subtidal areas; these species recolonize the inter tidal zone each spring as light
levels increase and ice dissipates.
In general, the studies indicate that subtidal plant and animal assemblages are more abundant and more diverse than are those in
the inter tidal zone. These differences reflect the greater stability and lower stress of subtidal environments, compared to inter tidal
environments where wave action, large temperature and salinity shifts, and seasonal ice gouging exer t stronger influence.
Benthic organisms at the shallowest depths tended to be relatively sparse. Soft substrates in the subtidal zones are dominated by
burrowing organisms, mainly tube-dwelling suspension feeding worms while rocky or coarse substrates are dominated by attached
or mobile organisms. Common attached inver tebrates include sponges, hydroids, sea anemones, and bryozoans. Common mobile
inver tebrates include species of snails, chitons, nudibranchs, crabs and sea-stars. Few bottom-dwelling (demersal) fish were
observed on dive transects, while bottom-oriented fish such as the whitespotted greenling, starry flounder, and juvenile flatfishes
are relatively common in the trawl catches.
The nearshore zones of Iliamna and Iniskin bays are used seasonally by numerous species of fish and macroinver tebrates as
rearing areas, migration corridors, and places of refuge from deepwater predators. The number of species and total numbers
of fish in the nearshore community expands from late-April through July, declining somewhat in August, increasing somewhat
in September, and declining again by October. Abundance data clearly indicate that the most prevalent fish use of the shoreline
areas is as a nursery for juvenile salmon and, on occasional years, juvenile Pacific herring.
Offshore sampling by bottom trawl revealed a substantially different fish community than that found in the nearshore. More
than 30 species of fish were observed but, like the nearshore community, this assemblage was dominated by just a few species,
Yellowfin sole and snake prickleback combined to make up more than 60% of all fish captured in the trawl.
Generally, there are relatively few inver tebrates in beach seines, with the exception of occasional high catches of mysids
(a type of shrimp) in inner Iliamna Bay. In contrast, trawl sampling captured numerous macroinver tebrates. In 2005, 2006 and
2007, more than 80 species were captured, with pandalid, cragonid and hippolytid shrimp species making up approximately 80%
(by number) of all inver tebrates caught in these sampling events.
The Marine Nearshore Fish and Benthic Invertebrate data report, released as part of the Pebble Partnership’s Pre-
Permitting Environmental & Socio- Economic Data Report Series, are available online at www.pebblepartnership.com.
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