|Larval Fish Identification and Abundance|
Final Report to CIAP and BOEM:
Busby M. S., Duffy-Anderson, J. T., Mier, K. L., Tabisola, H. 2015. Icthyoplankton Assemblages and Distribution in the Chukchi and Northern Bering Seas 2012-2013. US Dept. of the Interior, Bureau of Ocean Energy Management, Alaska OCS Region. OCS Study BOEM 2011-AK-11-08 a/b. 38 pp. – DRAFT REPORT
Ichthyoplankton surveys have become an integral component of ecosystem studies in the Pacific arctic over the past decade. In summer 2012 and 2013, large scale fisheries oceanographic surveys that included ichthyoplankton tows were conducted in the northern Bering and eastern Chukchi Seas as part of the Arctic Ecosystem Integrated Survey (Arctic Eis). Collections of pelagic fish eggs determined locations of spawning centers for Limanda spp. (probably yellowfin sole L. aspera) nearshore of the Seward Peninsula and Bering flounder (Hippoglossoides robustus) to the west and offshore from Point Barrow in 2012. Similar but less pronounced trends in egg distribution were observed in 2013. Spatial and temporal analyses of larval fish abundances determined that yellowfin sole (Limanda aspera) was the most abundant larval fish caught followed by Arctic cod (Boreogadus saida), an important forage fish in the food web of the Arctic ecosystem. Cluster analyses showed L. aspera to be the dominant component of a southern, nearshore assemblage strongly associated with the northward moving Alaska Coastal Current (ACC) characterized by comparatively warm, low-salinity water. Boreogadus saida larvae dominated a more northern assemblage in close proximity to the ice edge and were more abundant in 2013 than 2012. Larvae of the forage fish species capelin (Mallotus villosus) and Arctic sand lance (Ammodytes hexapterus) were important assemblage components in 2012 and 2013, respectively.
In development with collaborations from other studies to expand the data set and synthesis.
Larval fish samples from 2012 were returned from the Plankton sorting and identification Center in Szczecin, Poland and cross-checked within our team of experts at NOAA/AFSC to verify identifications.
We have created a geo-referenced database of fish larval numbers and catch-per-unit-effort of all major ichthyoplankton taxa by station for 2012. Further analysis will include maps of catch-per-unit-effort by major taxon relative to water mass structure in 2012 and 2013. We anticipate a manuscript on distribution and assemblage structure of ichthyoplankton in the Chukchi Sea.
|2012 and 2013 Preliminary Results|
After verifying identifications of the fish larvae we can first identify the major taxa in each region of our study area. Figure 1 represents results of a SIMPER analysis for the Chukchi and Northeast Bering Seas. A SIMPER – or Similarity Percentage – analysis is a simple method for assessing which taxa are primarily responsible for an observed difference between groups of samples. In this case, it represents differences between north and south of Bering Strait. It appears the majority of differences appear to be presence/absence of two species, Bering Flounder and Yellowfin Sole, as well as an overall higher number of taxa represented in the Chukchi Sea.
Review of Basic Water Masses: Analysis of distribution of major water properties revealed presence of three major pelagic habitats: well mixed warm (>7°C) and less saline (<31 psu) nearshore with surface pools of even fresher (<27 psu) water, well stratified offshore with cold (<1.5°C) and saline (>32 psu) bottom layer extended over the western shelf, and very cold (<1°C) and less saline (<30 psu) water observed in the northeastern Chukchi Sea (provided by Alexei Pinchuk).
Capelin larvae were present in the both Chukchi and northeast Bering Seas during the 2012 Arctic Eis Survey (Figure 2). They appear to occupy the nearshore habitat in high abundance and extend as far north as 68 deg North. In comparison, adult Capelin were also distributed region-wide, concentrated south of Bering Strait while being mostly absent or in low abudance in the northern Chukchi Sea.
Arctic Cod larvae and juveniles were present only in the north Chukchi Sea during the 2012 Arctic Eis Survey (Figure 3). They appear to occupy both nearshore and offshore habitat north of 70 deg in high abundance. This likely is associated with the very cold, less saline water mass in the northern region. In comparison, adult Arctic Cod catch included two size clades: 1) small young-of-year (~3-5cm length) fish which were highly abundant over the same northern region, and 2) large adults (>~10cm length) which were absent accept for a small pocket in Norton Sound south in the NBS.
Bering Flounder and Limanda spp. eggs (Figure 4) and larvae (Figures 5 and 6) were present in both the Chukchi and N. Bering Seas during the 2012 Arctic Eis Survey. Interestingly, the differences in catch location of eggs and larvae within and between species exhibits possible source and sink locations for early and late larval stages. Figure 4 shows egg catch for both species; which shows complete spatial separation of eggs between species at about 70 deg North. In contrast, both species larval forms occur south of those egg locations (Figures 4 and 5). This could be a reflection of egg (and larval flow) northward with the oceanographic currents from adult spawning populations in the south. More study is needed to address this new finding.