Environ Biol Fish https://doi.org/10.1007/s10641-017-0684-0 Distribution and habitat associations of the California moray (Gymnothorax mordax) within Two Harbors, Santa Catalina Island, California B. A. Higgins & R. S. Mehta Received: 14 March 2017 /Accepted: 11 October 2017 # Springer Science+Business Media B.V. 2017 Abstract While kelp forests are some of the best- higher densities of morays, while northern facing sites surveyed ecosystems in California, information on cryp- showed more size structuring. We show how the struc- tic inhabitants and their role within the community are tural complexity of the rocky reef habitat in an already lacking. Kelp itself provides overall structure to the diverse kelp forest ecosystem, can support a high bio- habitat; however the rocky reef to which the kelp at- mass of a cryptic elongate predatory fish. taches is known to provide additional structure for cryp- tic species. Gymnothorax mordax, the California moray, Keywords Catalina Island . CPUE . Muraenidae . is an elusive predatory species that is considered abun- Habitat . Gymnothorax dant in the waters around Catalina Island. However, no life history data exists for this species. We examined habitat composition, relative abundance, size pattern Introduction distributions, and biomass of G. mordax within Two Harbors, Catalina Island. Habitats were sampled using Kelp forests are considered one of the most diverse and a combination of baited trap collection and transect productive ecosystems in the marine environment (Mann surveys using SCUBA. A total of 462 G. mordax were 1973;Christieetal.2003) having strong recreational and captured, primarily in shallow (< 10 m) waters. Individ- economic significance to society (Simenstad et al. 1978; uals of G. mordax were associated with mostly boulder Erlandson 2001; Steneck et al. 2002). Therefore, it is not and cobble substrates. Measurements of relative abun- surprising that some of the most well-studied marine dance and density indicate that G. mordax is more communities are found within kelp forests (Steneck prevalent than reported in previous studies. We also et al. 2002;Graham2004; Allen et al. 2006). Despite discovered that the 6 trapping sites from which all the large body of literature on the life history of the morays were collected, differed in size structuring and icthyofauna and their associated habitats found within density while the relatively high biomass did not change the neritic waters of coastal systems, data on the more across sites. In general, southern facing sites exhibited sessile and cryptic vertebrate species within the kelp forest ecosystem are lacking and often influenced by Electronic supplementary material The online version of this article (https://doi.org/10.1007/s10641-017-0684-0) contains more conspicuous species (Allen et al. 1992; Willis and supplementary material, which is available to authorized users. Anderson 2003;Graham2004; Sandoval 2005). : While the monitoring of kelp forest fish populations is B. A. Higgins (*) R. S. Mehta important for ecosystem health, it presents numerous chal- Department of Ecology and Evolutionary Biology, Coastal lenges (Harvey et al. 2004). Fish populations are frequent- Biology Building, University of California Santa Cruz, 115 McAllister Way, Santa Cruz, CA 95060, USA ly assessed using presence/absence data to understand e-mail: [email protected] overall abundance and diversity patterns. These data are Environ Biol Fish typically collected using a variety of techniques, such as et al. 1989). Anguilliform elongation in fishes is thought band transects, random point contacts, visual transects, and to promote a burrowing or crevice dwelling lifestyle roving SCUBA diver counts (Davis et al. 1996; Stephens (Smith 2012). Additionally, densities of tropical moray et al. 2006). Not surprisingly, these visual censuses are species were positively associated with structural com- conducted during daylight hours and therefore abundance plexity (Gilbert et al. 2005). Similarly, rocky bottom and density data is more commonly reported for diurnal substrate was described as the ideal habitat for the fish populations (Ebeling and Bray 1976). Elusive and Mediterranean moray eel (Muaena helena)(Matić- cryptic diurnal species such as burrowers and nocturnally Skoko et al. 2011). Previous studies of G. mordax in active species are often excluded from such census data. Catalina suggest that the majority of their activity occurs For example, small cryptic diurnal species such as the during the night (McCleneghan 1973;BH&RSMpers. blue-banded goby (Lythrypnus dalli) and spotted kelpfish obs.). Therefore, because of their body shape and re- (Gibbonsia elegans)werereportedtobeuptofourtimes duced activity during daytime hours, we hypothesize as dense as conspicuous fishes. Although their biomass that habitat characteristics that promote structural com- may not be large, these species are thought to double the plexity will strongly influence where individuals of ichthyofaunal diversity in the system (Allen et al. 1992). G. mordax are found. As nocturnally active species often take refuge during Roughly 10–15% of the Southern California coast is daylight hours, the size of their populations and the classified as rocky shoreline (Stephens et al. 2006). resulting effects upon their community are unstudied However, the habitat structure of the Southern Califor- (Helfman 1986). Furthermore, nocturnal communities nia offshore islands (e.g., Catalina) consist largely of tend to have a higher relative abundance of predatory rocky shorelines, effectively doubling the amount of species than diurnal communities (Helfman 1986; hard bottom rocky reef and kelp habitat off Southern Hobson and Chess 1986), suggesting that crepuscular California (Froeschke et al. 2006;Stephensetal.2006). and nocturnal species may play an important role in shap- Thus, while the general habitat composition of the near- ing ecosystems, especially trophic dynamics. shore bathymetry around Catalina has been examined The California moray eel (Gymnothorax mordax) (see Seafloor Mapping Lab, California State University is the only muraenid found off the coast of Califor- Monterey Bay), it lacks the detail necessary to under- nia. The distribution of G. mordax extends from just stand moray habitat associations. Therefore, we know north of Santa Barbara to Santa Maria Bay in Baja little about how habitat characteristics (e.g., rocky reef, California (Fitch and Lavenberg 1971; Eschmeyer sandy bottom, etc.) influence the distribution of et al. 1983). Gymnothorax mordax is an elusive G. mordax. predatory species considered abundant in the waters While habitat characteristics are important during around Catalina Island (Fitch and Lavenberg 1971, and after settlement, the broad distribution of b) but limited data exists on its natural history (Fitch G. mordax around Catalina is likely influenced by the and Lavenberg 1971). The combination of a cryptic strength and directionality of the currents that are hy- lifestyle and the lack of a commercial fishery has pothesized to bring long-lived propagules from warmer, enabled morays, in general, to remain virtually un- southern waters, primarily during El Niño events detected in standard underwater visual surveys (McCleneghan 1973). We recently showed that El Niño (Gilbert et al. 2005). However, Froeschke et al. events contribute to the dispersal and subsequent re- (2006) included G. mordax in their dataset when cruitment of individuals of G. mordax to Catalina Island examining the effects of a Marine Protected Area (Higgins et al. 2017). Therefore, as current flow pre- (MPA) on fish populations. Despite the presumed sumably influences larval settlement, we anticipate dif- importance of cryptic predatory species, G. mordax ferences in adult size structuring among coves. As Cat- has rarely been incorporated into Southern Califor- alina is well nested within the Southern California Eddy nia kelp forest studies. In fact, no published study to (SCE), the coves on the leeward side of the island are date has focused on examining the distribution and more likely bathed in waters moving from southwest to relative abundance of G. mordax in the Southern northeast (Cowen 1985; Hu and Liu 2002). Thus, we California kelp forest ecosystem. predict that the coves most exposed to westerly currents Similar to all members of the Anguilliformes, morays will host G. mordax populations with greater size struc- (Muraenidae), exhibit an elongate body plan (Böhlke turing, as these are the sites first encountered by larvae. Environ Biol Fish To provide first-time data for a resident nocturnal between 18:00–19:00 h and baited with frozen ancho- predator, we organized our efforts to conduct a trapping vies, which were placed into perforated plastic bottles study along the western side of Catalina Island. In doing allowing odor to serve as an attractant while prohibiting so, we address the following questions: 1) Which char- access to the bait. acteristics within a kelp forest ecosystem is most asso- ciated with California moray eels?, 2) What are the Habitat assessment relative abundances and density estimates for moray populations in Two Harbors?, and 3) Based on what Within two hours of trap deployment, a team of we know about the exposure of leeward coves to incom- SCUBA divers descended upon the traps to survey ing current flow, do we see size structuring of morays the adjacent habitat structure. Initial trap depth was across coves? recorded, after which the divers conducted