Abstract
Pacific Herring (Clupea pallasii) as a species is a microcosm of the biodiversity conservation and restoration challenges facing our time. Overfishing is a global concern to the point of being considered an extinction crisis for particular fisheries. Understanding how, where, and when a particular species reproduces may be critical to understanding how a species responds to fishing pressure. The Pacific Herring is a small pelagic fish of the family Clupeidae. It is found throughout the Northern Pacific Ocean and has a North America range from Alaska to Baja Mexico. The Pacific Herring fishery in Tomales Bay has been closed to commercial fishing since 2007 because of overfishing, market price decline, and low fishing effort. This closure provided an opportunity to gain insight into the spawning habits and ecological context of spawning Tomales Bay Pacific Herring living under low fishing pressure. It has been long noted that herring tend to spawn in eelgrass (Zostera marina) meadows, but the extent of this dependency has not been thoroughly examined. So, it becomes essential to clarify and quantify the role of eelgrass as a spawning substrate for herring. Reported here are the results of a two-year field study of Pacific Herring spawning activity (2016 -2018) in Tomales Bay investigating the following question: Do Pacific Herring prefer natural eelgrass for spawning compared to other natural or artificial substrates? Eelgrass is the dominant vegetation in Tomales Bay. It is a submerged seagrass found nearshore, ranging from Alaska through Baja California and is found around the globe. Two nearshore westerly sites in Tomales Bay were selected for this project: Sacramento Landing and Chicken Ranch Beach. Experimental intertidal and subtidal spawning sites were built using three different types of artificial substrate and installed at each site. The experimental substrates were Artificial Eelgrass, Concrete, and the existing Bottom (bare, sand, silt, or rock). The spawning data from the experimental substrate meadows were compared to natural eelgrass meadows near the study sites. Herring roe abundance and density (layering of roe) were measured on each substrate. Potential predators on or near the sites were counted during herring roe data collection and environmental conditions were recorded (tide, turbidity, and temperature). Results from data analysis with Repeated Measures One-Way ANOVA and with multiple comparisons using Sidak’s multiple comparisons test strongly support the hypothesis that spawning Pacific Herring roe is mostly found on natural eelgrass compared to alternative substrate measured by the accumulation of eggs after spawning events. This finding indicates that herring will spawn in natural eelgrass beds even in the presence of predators. Findings from this study support local eelgrass conservation and restoration efforts as an important component of Pacific Herring fisheries preservation and sustainability .