Kokanee salmon lake acidity. As a result, the kokanee was believed to have gone extinct in the 1940s. In 2011 a few fish were found in an isolated lake on Mount Fuji. The Japanese kokanee varies from its sea-going sockeye relative in a few ways. The black kokanee breeds in March at a depth of 30–40 feet, while sockeye salmon breed in the fall and have a different number of gill rakers than the kokanee. In addition, the black kokanee is much darker in color than the sockeye or any other kokanee population. The fish has been introduced to different lakes around
Environmental issues with salmon 59 years of catch and escapement data of Bristol Bay sockeye to determine age and size at maturity trends attributable to the selectivity of commercial gillnet harvests. The study found that the larger females (>550 mm) of all age classes were most susceptible to harvest. The study suggests that smaller, younger fish were more likely to successfully traverse the gillnet fishery and reproduce than the larger fish. The study also found that the average length of sockeye harvested from 1946–2005 was 8 mm larger than the sockeye who escaped the gillnet fishery to spawn, reducing the fecundity of the average