In partial fulfillment of his MS in Marine Biology, Andy Padilla will be defending on February 24, 2015 at 12:30pm in Duckering room 531. The title of his thesis is "Using otolith strontium isotopes to elucidate population structure and movements of Bering cisco (Coregonus laurettae)."
Methods for stock discrimination and tracking the movements and distribution of fishes have often involved expensive field logistics, a problem compounded in remote regions such as Alaska. An alternative approach is to use the chemical signatures preserved in otoliths, or ear bones, of teleost fishes to discriminate stocks or to track the movement history of fish. I used the strontium isotope signature (87Sr/86Sr) preserved in the freshwater portion of otoliths taken from Bering cisco Coregonus laurettae to identify their natal river of origin. Bering cisco spawn in freshwater rivers and rear in coastal marine waters (anadromous). Only three known spawning rivers exist worldwide, the Yukon, Kuskokwim, and Susitna rivers. Rearing occurs commonly in coastal estuaries and lagoons on the Arctic coast of Alaska, Yukon-Kuskokwim Delta (Y-K Delta), and rarely on the Alaska Peninsula. Currently, a commercial fishery targeting Bering cisco (Coregonus laurettae) is occurring in the Yukon River, Alaska. Managers believed that two of the three populations were being harvested in the fishery. To determine the likelihood of a mixed-stock fishery, I used strontium isotope ratios (87Sr/86Sr) from the freshwater region of otoliths, from spawning adult Bering cisco of known origin (n= 82), to create a baseline. The baseline was then used to classify commercially harvested Bering cisco (n=139) and determine the stock composition of the fishery. The majority of the commercial samples (n=136), with >90% posterior probability, were classified as Yukon River origin. However, 0.7% (n=1), and 1.4% (n=2) of the commercial samples were classified as originating from Kuskokwim River and Susitna River, respectively. In addition, the baseline was also used to classify Bering cisco from three coastal rearing areas (Alaska Arctic coast, n=48; Y-K Delta, n=70; and the Alaska Peninsula, n=8). Approximately 96% of the fish from rearing areas had strontium isotope signatures that were consistent with a Yukon River origin. These data demonstrate the wide-spread coastal distribution of Bering cisco, with some travelling more than 4,500 km between coastal rearing and spawning habitats. This approach illustrates that strontium isotopes can be used to determine the natal river and migration behavior for Bering cisco of unknown origin.