The surfperches in the genus Amphistichus of the west coast of North America are important mesopredators in the sandy beach community. However, knowledge of their ecology is limited due to the challenges of collecting ecological data from an organism that is mostly active in the crashing surf. Basic life history data is available for two of the three extant species. The third, Amphistichus koelzi, has gone essentially unstudied, despite its large size and contribution to recreational and commercial fisheries, because presence of A. koelzi is less predictable and the species is collected at much lower frequencies than the other two species, making it something of a ‘mystery’ fish. We explored the life history and ecology of A. koelzi by gathering growth and reproductive data at multiple points in time and multiple localities spanning the majority of their geographic range, to obtain evidence for ecological partitioning among the three species of Amphistichus. We sampled with traditional hook-and-line methods and engaged anglers to obtain specimens, from which we took data on size, age, reproductive status, brood size, and size of offspring. Our project was a collaboration between State, Federal and university researchers with diverse missions and research perspectives.
Specific Results: We took data on over 400 adult fish and 1,000 embryos at sites from Monterey to Humboldt Counties, California. Male A. koelzi are reproductively active between October and December and females carry embryos between December and May. Females require at least two years to reach sexual maturity. Timing of embryonic development appears to vary with latitude, where northern populations develop later. We found that the reproductive schedule of A. koelzi appears to closely track that of its sister species, A. argenteus, but occurs up to six months earlier than A. rhodoterus, the Northernmost species.
Implications for ecology: A. argenteus and A. rhodoterus are allopatric, but A. koelzi is sympatric with one or the other species over its entire range. Because the reproductive schedule of A. koelzi overlaps with A. argenteus, ecological separation may instead arise from differences in foraging or microhabitat. Future studies on diet and microhabitat use will shed light on the ecological roles these species play in the sandy surf. Furthermore, the observed latitudinal effect on reproduction suggests that these species may be subject to effects of climate change.