SPATIAL DISTRIBUTION of SOUTHERN CALIFORNIA BIGHT DEMERSAL FISHES in 2008 Eric F

MILLER AND SCHIFF: SOUTHERN CALIFORNIA DEMERSAL FISH COMMUNITY CalCOFI Rep., Vol. 52, 2011 SPATIAL DISTRIBUTION OF SOUTHERN CALIFORNIA BIGHT DEMERSAL FISHES IN 2008 ERIC F. MILLER KENNETH C. SCHIFF MBC Applied Environmental Sciences Southern California Coastal Water Research Project 3000 Red Hill Ave. 3535 Harbor Blvd., Suite 110 Costa Mesa, CA 92626 Costa Mesa, CA 92626 P: 714-850-4830 F: 714-850-4840 E: [email protected] ABSTRACT (Bograd and Lynn 2003). Both low- and high-frequency In an effort to better characterize the spatial dynam- variability has been linked to marked changes in the ics of the assemblage, the demersal fish communities abundance and distribution of fishes, including demer- throughout the Southern California Bight (Point Con- sal species (Mearns 1979; Stull and Tang 1996; Perry ception, California to the United States-Mexico border) et al. 2005; Hsieh et al. 2009). Recent discoveries of were sampled in 2008 utilizing standardized methods an expanding oxygen minimum zone (OMZ) in the under an interagency program. Otter trawl sampling was Eastern North Pacific basin, and its negative impact conducted in habitats ranging from select bays and har- on demersal and benthic life raises additional concern bors out to the upper continental slope. Pacific sanddab (Levin 2003; Grantham et al. 2004; Powers et al. 2005; (Citharichthys sordidus) was the most commonly caught Bograd et al. 2008; Chan et al. 2008; Diaz and Rosen- species and contributed the greatest biomass. The catch berg 2008; McClatchie et al. 2010). Within the SCB, compositions at each site generally segregated along Bograd et al. (2008) found areas with the highest rate depth gradients, but not latitudinal gradients except for of dissolved oxygen decline along the inner and middle within the bay/harbor strata. The largest catches were shelves near the greater Los Angeles and Orange County, recorded in the central area, which includes the Santa California, coastlines. Monica Bay and the Los Angeles–Long Beach harbors. While fishes typically exhibit population level Offshore densities peaked along the middle and outer responses to environmental variation (Juan-Jordé et al. shelf (30–200 m depth). Species diversity was compar- 2009), these oscillations can be exaggerated or masked atively stable and elevated along the deeper portions by anthropogenic impacts such as harvesting (Brander of the continental shelf relative to the inner shelf (<31 2007; Perry et al. 2010; Hidalgo et al. 2011), habitat m depth) with the minimum diversity recorded in the alteration (Dayton et al. 1995), and ocean discharge from southern portion of the inner shelf. both point (e.g., wastewater discharge) and non-point sources (e.g., storm drain; Allen 2006a). Historically, SCB INTRODUCTION demersal fish community changes were traced to effects The Southern California Bight (SCB) is a diverse of wastewater discharge through either altered com- area characterized by heterogeneous habitats (Dailey et munity demographics (composition, abundance, species al. 1993); the convergence of the cold southward flowing diversity, etc.) or prevalence of tumors and other physi- California Current and the warm poleward flowing Cal- cal abnormalities (Perkins 1995; Stull and Tang 1996; ifornia Countercurrent (Hickey 1992); a variable width Allen 2006a). While most wastewater discharge effects continental shelf; and multiple, densely populated, met- on the demersal fish community have subsided (Stull and ropolitan areas (e.g., Los Angeles, San Diego, etc.). Fishes Tang 1996; Allen 2006a,b), impacts of fishing and other within the SCB represent a transitional fauna indicative anthropogenic interactions with the coastal waters can of the dynamic environmental conditions present, with still be detected (Schroeder and Love 2002). Concerns species representative of the Oregonian and San Diegan over large, point-source ocean discharges resulted in per- biogeographic provinces commonly occurring in the mit-required demersal fish monitoring (Mearns 1979; area (Horn et al. 2006). Love et al. 1986; Stull and Tang 1996). Demographic Environmental conditions can fluctuate widely on indices (abundance, biomass, composition, etc.) on the annual to decadal scales, often related to larger scale demersal fish stocks of the SCB shelf are routinely moni- oceanographic phenomena affecting the California tored through this permit-required monitoring. Current such as El Niño Southern Oscillation (ENSO) Despite the level of effort devoted to monitoring, events (1997–98 ENSO; McGowan et al. 2003) or vari- however, little primary research documenting the soft- ability in the strength and position of the Aleutian Low bottom demersal fish communities of the SCB beyond 80 Miller Schiff.indd 80 11/7/11 8:33 PM MILLER AND SCHIFF: SOUTHERN CALIFORNIA DEMERSAL FISH COMMUNITY CalCOFI Rep., Vol. 52, 2011 site-specific programs (see Stull and Tang 1996) has been 33.5–34˚N = central, and <33.5˚N = south. Hencefor- published since Love et al. (1986), which was limited to ward, shelf strata-region combinations (e.g., IS-S) are communities inshore of the 20-m isobath. Deficits in referred to as blocks (e.g., IS-S block) for simplicity. this information at a regional scale limit the detection of population responses to large scale perturbations such Sampling Methods as OMZ intrusion. McClatchie et al. (2010) modeled Sampling was completed during the summer (July– the predicted effect of OMZ on cowcod (Sebastes levis) September, 2008) with 7.6-m head-rope semiballoon habitat, but abundance information will be needed to otter trawl nets fitted with 1.25-cm cod-end mesh dur- evaluate their predictions of population-level responses. ing daylight hours. Trawls were towed along open-coast As an example, Grantham et al. (2004) was able to use isobaths for ~10 min (~5 min in bays and harbors) at previously recorded demersal species abundance data 0.8–1.0 m/sec. These tows were designed to cover an collected near an oceanographic monitoring transect estimated distance of 300 and 600 m for 5 and 10 min to report on the catastrophic effects of hypoxia on the trawls, respectively. The actual trawl distance was cal- demersal resources off the Oregon coast. culated from the difference between the start and stop An integrated, area-wide sampling effort utilizing fishing GPS coordinates recorded on the deck of the standardized methods can provide the necessary robust towing vessel. These acted as a proxy for the net’s rela- snapshot of baseline conditions to not only provide con- tive position. It was assumed the net remained on the text for site-specific monitoring results but also, after bottom and fishing the entire time. Upon retrieval, repeated surveys, provide tractable evidence of commu- catches were sorted, identified to species, enumerated, nity changes (Bertrand et al. 2002). The Southern Cal- and batch weighed to the nearest gram (g). Each sta- ifornia Bight 2008 Monitoring Program (Bight 2008) tion was sampled once per survey. Catches from sam- was conducted to provide this general overview of the pling events aborted due to equipment malfunction or SCB demersal fish community spatial dynamics. Utiliz- protocol violations were discarded and the station was ing the Bight 2008 results, this study aims to describe resampled, if possible. the spatial pattern of the SCB soft-bottom demersal fish stocks with a specific goal of characterizing the assem- Data Analysis blage variability between discrete depth strata and lati- The analysis focused on the demersal communities; tudinal regions, for both the community as a whole but therefore pelagic, midwater fishes (Allen and Pondella also at species-specific levels. Such information is lack- 2006), e.g., northern anchovy (Engraulis mordax), were ing in the recently published literature and will likely excluded as their catches likely include sampling dur- benefit future evaluations of the various anthropogenic ing midwater deployment or retrieval (Biagi et al. 2002). and environmental factors previously mentioned, e.g., Underwater measurements by Environmental Qual- the expanding OMZ. ity Analysts and Marine Biological Consultants (1975) determined the 7.6-m trawl net used in all four Bight MATERIALS AND METHODS surveys spread 4.9 m, on average, while under tow and fishing. The area swept in this analysis represents the dis- Sampling Station Description tance trawled (m) × 4.9 m. Densities represent the abun- Demersal fish on soft-bottom habitat were sampled dance (biomass) per area swept (m2). at 143 stations by otter trawl across the SCB at sta- Mean density (count/1000 m2) for each species and tions using a probability based design (Stevens 1997) that its frequency of occurrence in individual trawl sam- selects sampling sites a priori among areas determined to ples were derived by shelf strata. The mean density by be free of obstructions (able to be sampled with an otter block (e.g. inner shelf south) for the 21 most abundant trawl) based on reviews of bathymetric maps (fig. 1). species caught across the three open coast shelf strata During the Bight 2008 planning, stations were segre- (inner, middle, and outer shelf). Based on the proba- gated into discrete shelf (depth) strata and latitudinal bilistic design, density by stratum was area-weighted groups. To account for differences between expected and using the ratio estimator approach following Thomp- actual depths at each sampling site, all open coast data son (1992): were reclassified after sampling into consistent shelf strata by actual sampling depth: 5–30 m = inner shelf (IS), n 31–120 m = middle shelf (MS), 121–200 m = outer ∑ (pi * wi ) shelf (OS), and >200 m = upper slope (US). Sampling i = 1 m = , results from bays and harbors remained classified into the n bay/harbor (BH) shelf strata. Within each stratum, latitu- ∑ wi dinal distributions were designated as: >34˚N = north, i = 1 81 Miller Schiff.indd 81 11/7/11 8:33 PM MILLER AND SCHIFF: SOUTHERN CALIFORNIA DEMERSAL FISH COMMUNITY CalCOFI Rep., Vol. 52, 2011 where: Similarities along the full latitudinal and depth gradi- m = Area-weighted mean density for stratum j.

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