Abstract
The California Grunion Leuresthes tenuis, a marine atherinopsid, makes spawning runs onto some of the busiest urban beaches of southern California. Eggs remain buried under moist sand, tidally emerged from water throughout incubation. Concern over the effects of human activities on beaches holding incubating fertilized eggs of L. tenuis prompted a need to assess spawning runs consistently through time. A new metric, the Walker Scale, focused on the peak of the runs, was developed to train citizen scientists, also known as community scientists. Reports of sightings were verified by scientists by locating buried clutches and collecting eggs at locations identified by volunteers. Reports between multiple observers from the same run were highly correlated, and also positively correlated with the density of clutches of eggs. Over the past two decades, the Walker Scale method has been used by thousands of volunteers as well as resource managers, environmental consultants, coastal projects, the US Army Corps of Engineers, and the California Department of Fish and Wildlife. This paper provides details about the method and its correct use by citizen scientists and professional biological monitors. The Walker Scale method is reliable, easy to understand, and the most effective method for assessing this elusive, charismatic fish.
Highlights
The California Grunion Leuresthes tenuis, a marine atherinopsid, makes spawning runs onto some of the busiest urban beaches of southern California
Out of water, spawning California Grunion are vulnerable to capture by animal and human predators (Martin and Raim, 2014; Martin et al, 2020a)
Efforts are underway to return the closed season to its original three months, based on data indicating a decline in the California Grunion population (Martin et al, 2020a)
Summary
The California Grunion Leuresthes tenuis, a marine atherinopsid, makes spawning runs onto some of the busiest urban beaches of southern California. S OUTHERN California beaches are prized for their recreational opportunities and natural beauty They are critical reproductive habitat for many organisms, including the California Grunion Leuresthes tenuis (Atherinopsidae; Robbins, 2006). This marine species rarely is seen except during its spectacular midnight beachspawning runs (Walker, 1952; Martin and Swiderski, 2001). Out of water, spawning California Grunion are vulnerable to capture by animal and human predators (Martin and Raim, 2014; Martin et al, 2020a) This is the only fish that can be observed and captured by people of all ages, without a boat, without fishing poles or nets, or gear of any kind. If not environmentally triggered to hatch, California Grunion eggs can survive buried in beach sand for up to 35 days (Martin, 1999; Smyder and Martin, 2002), delaying larval development until hatch (Moravek and Martin, 2011)
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