Ecological Assessment of the HMCS Yukon Artificial Reef Off San Diego, CA (USA)
Total Page:16
File Type:pdf, Size:1020Kb
Ecological Assessment of the HMCS Yukon Artificial Reef off San Diego, CA (USA) by Ed Parnell1 January 7, 2005 1Scripps Institution of Oceanography, Integrative Oceanography Division, University of California, San Diego, La Jolla, CA 92093-0227 Prepared for: The San Diego Oceans Foundation P.O. Box 90672 San Diego, CA 92169-2672 http://www.sdoceans.org Sponsor: California Artificial Reef Enhancement Program 1008 Tenth Street, Suite 298 Sacramento, CA 95814 http://www.calreefs.org Ecological Assessment of the HMCS Yukon Artificial Reef off San Diego, CA EXECUTIVE SUMMARY inception of the monitoring program. Many of the species that first colonized the ship were The San Diego Oceans Foundation sank the species whose ambits are large and which likely HMCS Yukon, a decommissioned Canadian move among nearby artificial and natural destroyer escort (~112m long), off San Diego in habitats. Secondary colonization of the ship is 2000 as an artificial reef to support diving ongoing and consists of fish that are residential recreation, fishing, scientific research and and have recruited to the ship and species education. The Foundation then developed and whose ambits are generally smaller than the conducted a volunteer based monitoring early colonizers but whose abundances are program of the Reef to determine the variable. colonization of marine life on the ship over time and to gauge its ecological effects. The Sheephead and boccacio, two species that are monitoring program is still ongoing and the highly targeted by commercial and sports Foundation plans to continue the program fishers, successfully recruit onto the Yukon. indefinitely. Here, I report the results of the Blacksmith, a non-targeted species, also appear monitoring program four years after the to successfully recruit on the ship. Therefore, establishment of the Reef. the Yukon provides recruitment and nursery habitat for these species. In addition, Wreck The program consisted of volunteer divers Alley, the network of artificial reefs that the conducting fish counts on permanently Yukon is part of, may have synergistic beneficial established transect lines and photographing effects by increasing forage areas and by serving quadrats attached to the hull and deck. No data as stepping-stones for mobile species between were collected inside the vessel for safety natural habitats located to the north and south. reasons. The volunteer aspect of the program met with mixed success. The volunteer program Comparisons to natural habitat in La Jolla was successful as a pilot program for indicate that the implementing fish and invertebrate studies using fish population on trained volunteers. The results indicate that fish the Yukon is count data were consistent among the most presently experienced fish counters. However, because significantly less the study was voluntary, sampling effort was diverse. random. This was especially a problem for the However, an Juvenile boccacio photo quadrats, which were not conducted increasing trend frequently enough over an adequate period to in species detect temporal patterns other than seasonal. richness was Regular sampling frequency is recommended for observed which the future. appears likely to continue at least over the short The species composition of the fish community Terminal phase, sheephead on the Yukon has changed significantly since the term. Therefore, 2 Ecological Assessment of the HMCS Yukon Artificial Reef off San Diego, CA the fish community on the Yukon is still address the issue of whether the Reef was developing four years after reef establishment. beneficial for enhancing fish production over an The Yukon provides fish habitat that is a area larger than the ship. The controversy over combination of deeper kelp-forest and canyon- whether artificial reefs increase regional fish rim habitat in southern California. production or whether they lead to the concentration of fish into ‘kill zones’ and are The fouling community on the Yukon is also still therefore detrimental to fish on natural habitats developing. There are presently abundant is still the subject of much scientific debate. The populations of the anenomes Metridium spp. and role of the Yukon and the other artificial reefs in Corynactis californica over much of the ship. the area as enhancers or attractors is not known Comparisons of the fouling community, based on because no comprehensive studies have been quadrat photos and my observations, with conducted to specifically address this issue. studies of other artificial reefs in southern Therefore, comprehensive studies of this artificial California suggest that the fouling community on reef network are needed to determine whether the Yukon is not yet successionally mature. This these reefs are beneficial or harmful to natural is evidenced by the lack of late successional- populations. stage species such as gorgonians and turf algae. The algal community mainly consists of small BACKGROUND stipitate kelps, flat bladed kelps, mats of filamentous diatoms, and recruits of two species Artificial Reefs of surface-canopy forming kelps (Macrocystis pyrifera and Pelagophycus porra). Although the Fishers have used artificial reefs and other forms ship supports these kelps, the Yukon does not of habitat enhancement for centuries. The use of appear to provide suitable substrate to support artificial reefs has increased tremendously in the the development of a kelp forest because giant last fifty years intended both as a means of kelp cannot attach firmly to the hull. It is also mitigating human effects on marine ecosystems apparent that and as a means of disposal. As a tool for anti-fouling paint mitigation, artificial reefs are generally intended is precluding to mitigate overfishing and habitat degradation. colonization of Artificial reefs are also a by-product of other both human activities not intended for mitigation such invertebrates and as shoreline development (jetties, piers, and Metridum spp. algae on some breakwaters), energy production (e.g., oil rigs, areas of the hull. cooling systems), waste disposal (armored sewer pipes, ships), and military conflict (shipwrecks). Due to limited resources, the Most artificial reefs have been established to Yukon monitoring enhance marine resources. However, while there program was not is much evidence that artificial reefs can Corynactis californica designed to increase catch in the immediate vicinity 3 Ecological Assessment of the HMCS Yukon Artificial Reef off San Diego, CA (Bohnsack et al. 1991), there is still much that artificial reefs may be beneficial in southern scientific debate over the utility of artificial reefs California is provided by a bight-wide habitat for the enhancement of regional fish production valuation study (Bond et al. 1999) in which (e.g., Bohnsack 1989, Polovina 1991, Grossman shallow artificial reefs were second in habitat et al. 1997). Central to this debate is the so- value only to kelp forests. called ‘production-attraction’ controversy. This controversy is centered on the question whether Effective enhancement of fish production in artificial reefs actually increase regional southern California utilizing artificial habitats is production or whether they serve simply to still in its infancy and should be approached redistribute fish via attraction thereby using a staged process. First, studies testing concentrating fish into ‘kill zones’. It is likely that whether artificial habitats could be regionally there is a continuum between these extremes, beneficial using scientifically defensible pilot and every artificial reef lies somewhere along programs are needed. Then, if artificial habitats this continuum. The production/attraction appear beneficial, optimal designs for these debate is only relevant for mobile (non- habitats and networks of habitats must be residential) species for which redistribution is developed. These efforts are already well possible. There is ample evidence that artificial underway in Japan in which a federally reefs support residential and sessile (attached) subsidized artificial habitat program is an species (e.g., oil rigs, Wolfson et al. 1979, Love integral component of an optimal resources et al. 1999). Species most likely to benefit from management plan at the scale of the continental artificial reefs are those having limited natural shelf (Nakamura 1985, Grove et al. 1994). The habitat (Pickering & Whitmarsh 1997). ultimate goal of this program is optimal ‘farming’ Therefore, the assumption that fish production is of the entire shelf. While not advocating such an limited by resources provided by natural habitat approach in California, a better understanding of underlies the motivation for most artificial reef the ecological effects of artificial habitats is development (Patton et al. 1985). certainly needed. The Southern California Bight is presently Many artificial habitats have been established dominated by sand relative to historical throughout southern California but their interglacial periods when sea level was up to ecological effects are still poorly understood ~100 meters lower and the proportion of rocky- against the framework of the hard bottom was much greater than it is today attraction/production controversy mainly (Graham et al. 2002). Since most species of because the resources to study artificial habitats recreational and commercial interest are are extremely limited. Simply put, there are associated with hard bottoms in southern presently not enough resources to support California, it is likely that