Rockfish

Inside and out of the San Juan Islands Marine Preserves:
Demographics of nearshore rocky reef fish
By Eric Eisenhardt,
School of Aquatic and Fishery Sciences, University of Washington
(from Puget Sound Water Quality Action Team's
Puget Sound Notes Number 46, January-2002)

Introduction

Most research on marine reserves to date has taken place in tropical systems. Studies have shown temporal increases in abundance and size of fish in marine reserves on tropical reefs (Alcala and Russ 1990; Roberts and Polunin 1991), and export of adult biomass outside reserves (Russ and Alcala 1997). A handful of studies have tested the influence of marine reserves on nearshore rocky reef fish assemblages in temperate regions (McCormick and Choat 1987; Palsson 1998; Paddack and Estes 2000; Martel and others 2000). However, these temperate studies have relied on comparisons of "fished" and "reserve" sites (1) with little or no replication of treatments or (2) across limited time scales.

The San Juan Islands Marine Preserves are fishery reserves created by the Washington Department of Fish and Wildlife in 1990. They restrict all forms of fishing except for salmon, herring, and, in certain areas, crab (Murray 1998), and offer an opportunity to study the effects of harvest restrictions on rocky reef species. Anglers targeting salmon have little interaction with rocky reef fish, with the exception of lingcod, Ophiodon elongatus (K. Koski, personal communication). There is little or no bycatch associated with herring fishing. Crabs are fished with pots and usually in soft-bottom habitats.

Bottomfish angler trips in northern Puget Sound peaked between 1980 to 1983, and by 1994 the annual number of trips was down to early 1970s levels. A 10-fish bag limit for rockfish was enacted in 1983, and reduced to five fish in 1994. The current daily bag limit for rockfish is one fish. In 1992, the lingcod season was reduced from seven months to six weeks and minimum/maximum size limits were introduced. Directed commercial fisheries for rockfish using jig and troll gears were prohibited in the San Juans in 1984 (Palsson and others 1997). Trawling is allowed outside reserves, but rarely occurs in San Juan Channel, and has resulted in total annual rockfish landings of less than 100 pounds since 1994. No lingcod have been caught commercially during the last few years (W. Palsson, personal communication).

Data presented here were collected from six sites between July 27 to October 5, 2000. Historical data collected in San Juan Channel from 1974 to 1976 by Moulton (1977) are presented for comparison. The three San Juan Islands Marine Preserves in San Juan Channel that contain nearshore rocky reefs were selected as study sites. These were paired with non-reserve sites to provide similar bathymetry, substrate complexity, algal communities, and exposure to oceanographic processes within each reserve/non-reserve pair.

The eight target species for which data were collected included five rockfish: copper (Sebastes caurinus), quillback (S. maliger), black (S. melanops), yellowtail (S. flavidus) and Puget Sound (S. emphaeus); lingcod (O. elongatus), kelp greenling (Hexagrammos decagrammus), and striped surfperch (Embiotoca lateralis). These species are distributed over a gradient of susceptibility and desirability to local angler effort. They comprise the largest and most conspicuous members of the nearshore rocky reef fish assemblage in San Juan Channel. Due to space constraints, this paper will present data for three species: lingcod, copper rockfish, and Puget Sound rockfish. See Eisenhardt (2001) for additional information.

It should be noted that this study surveyed 0 to 20 meters depths. The species studied are also known to inhabit deeper waters. In addition, the San Juan Islands Marine Preserves encompass depths greater than the depth range covered by this study. Therefore, these results should not be extrapolated to all depths.

Methods and materials

Data were collected via 25 meters by two meters visual band transects by two researchers using SCUBA. Data collected for each transect included species, length (total length to nearest centimeter), and depth for all target species sighted, as well as habitat information, including substrate complexity, slope, and percent cover of rock, algae, invertebrates, and sediment. Forty-eight transects were completed at each site. See Eisenhardt (2001) for detailed methods. Fish densities were computed as fish per 100 square meters and statistics were computed using SYSTAT 10.

Results

Length-frequency distributions were used to compare demographics of fish populations inside and out of reserves in 2000 to the 1970s. Total numbers of fish in reserves and non-reserves provide abundance estimates, as these data resulted from equal sized areas surveyed. Area surveyed for historical data was different. Therefore, 1970s abundance should not be compared to 2000 abundance using these figures. For results of population densities over time, see Eisenhardt (2001, in press).

The data are species specific. Statistical anyalyses show a greater mean length (two-sample t-test: p < 0.001) and greater density (3 x 2 ANOVA: F = 10.487, p = 0.001) for copper rockfish in reserve sites compared to non-reserve sites. Large copper rockfish (larger than 38 centimeters), which have been reported to reach 35 years in age (Richards and Cass 1986), have virtually disappeared since the 1970s. Greater mean length (two-sample t test: p < 0.001) was found for lingcod in reserves compared to non-reserves, but no statistically significant difference in density of lingcod was found, due to the high variability in lingcod densities – despite 35 percent greater mean density of lingcod in reserves. In addition, 43 percent of lingcod sighted in reserves were greater in length than 50 centimeters, compared to only 17 percent in non-reserves. Length at 50 percent maturity for male lingcod is 51.3 centimeters (Jagielo 1994). Puget Sound rockfish showed an opposite trend with a greater mean length (two-sample t: test p = 0.001) in reserves, but greater density (3 x 2 ANOVA: F = 10.487, p = 0.005) in the non-reserve sites. Habitat variables were similar between each reserve/non-reserve pair. Further discussion of results for each of these species and possible mechanisms follows in the discussion section.

Discussion

Copper rockfish are a commonly targeted bottomfish and are often caught as bycatch by anglers targeting lingcod. The virtual disappearance of copper rockfish larger than 38 centimeters (a 45 centimeters individual was sighted during the 2000 survey) is important to note, as fish this size were more common in the 1970s (Moulton 1977). This trend indicates increased mortality of larger, more fecund individuals since the 1970s, almost certainly due to fishing pressure. This study shows that to regenerate an abundance of copper rockfish individuals larger than 38 centimeters, protection measures will need to be in place for at least 10 years. This is logical for a species that can live to be 35 years old. Given more time, copper rockfish larger than 38 centimeters will probably become more abundant in reserves.

While there were reproductive adult copper rockfish in both reserves and non-reserves, densities were greater in reserves – especially for larger length classes. Given the non-linear increase of copper rockfish fecundity as a function of length (DeLacy and others 1964; Washington and others 1978), reserves contain greater reproductive potential than non-reserves. The term "reproductive potential" is used to describe the number of eggs produced per area of habitat by a population (Paddack and Estes 2000).

During the spring of 2000, Sebastes larvae identified as copper/quillback rockfish complex were most abundant in the middle of San Juan Channel, and abundance increased with increasing distance from shore (Chasco and others 2000). This trend indicates that planktonic larvae of the copper/quillback rockfish complex in San Juan Channel are probably contained in a common larval pool. Therefore, larvae are probably dispersing from where they are released to this common pool, and then settling out as juveniles throughout San Juan Channel. If this is correct (and since fish in reserves seem to contribute a disproportionately greater share of larvae to the common pool than the area of rocky reef habitat encompassed by reserves indicates) reserves appear to supply a disproportionately large share of copper rockfish larvae to both reserve and non-reserve areas.

Lingcod are commonly targeted by anglers and are one of the most highly prized and sought after bottomfish in San Juan Channel. The low end of the legal size limit for lingcod is 26 inches (or 66.04 centimeters), the same size at which greater fish densities in reserves begin to appear. The distribution of lingcod in reserves is similar to that found in San Juan Channel during the mid-1970s, while the distribution in non-reserves is lacking larger individuals. This is strong evidence that removals by anglers fishing in non-reserve areas structure the demographic pattern of lingcod in San Juan Channel.

Lingcod inhabiting nearshore rocky reefs seem to be predominantly males, while females reside in deeper water most of the year and enter shallower nearshore waters only briefly to spawn (T. Jagielo, personal communication). Egg nests have been sighted via SCUBA in the reserves; however, most or all of the broodstock may not typically be within working SCUBA depths and are possibly out of the reserve boundaries altogether (except during spawning). Still, assuming larger males guard larger egg masses during the nesting season (as seen by this author), larger males should have a disproportionately large relation (on a per-fish basis) to the reproductive potential of the population. In this study, lingcod were significantly larger in reserves. Therefore, the reserve areas could be contributing disproportionately more to the reproductive potential of the population than the amount of area contained in reserves would indicate.

Despite possible disproportionate contribution to lingcod reproductive potential from reserves, both reserves and non-reserves have similar densities of subadult recruits, that is densities of individuals less than 50 centimeters were similar in reserves compared to non-reserves.

Young-of-the-year lingcod have been found initially in soft-bottom areas, for example bays and coves, and then disappearing from this habitat and beginning to appear in nearshore rocky reef habitat sometime before the end of their first year. Due to the rocky nature of the San Juan Channel study area, shallow soft bottom habitat is scarce. Therefore, it is likely that lingcod found on different rocky reefs (including site pairs in this study) initially recruited to the same soft-bottom areas. If reserves are contributing disproportionately more reproductive potential than a per-area basis would indicate, it would follow that lingcod in reserves are augmenting recruitment outside reserves.

Puget Sound rockfish are seldom caught by anglers because they feed on plankton (Beckman 1995) and their mouths are too small for a typical bottomfishing hook (B. Miller, personal communication). They reach a maximum size of 18 centimeters (Beckman 1995). Fishing is probably not structuring the demographics of this species. The greater abundance of Puget Sound rockfish in non-reserves versus reserves is probably due to increased predation of Puget Sound rockfish inside reserves by the more abundant and significantly larger lingcod inside reserves. Gut contents of lingcod revealed Puget Sound rockfish, and lingcod were often sighted in association with aggregations of Puget Sound rockfish (W. Palsson, personal communication).

The reserve network seems to play an indirect yet major role in regulating the density and mean size of Puget Sound rockfish at the various sites, since reserves appear to regulate the demographics of lingcod at different sites. Human influences appear to be structuring ecosystems directly (in the case of lingcod) and indirectly (in the case of Puget Sound rockfish). There could be other, unknown, indirect impacts on other species, for example killer whales (Orcinus orca) and harbor seals (Phoca vitulina richardsii).

References Cited

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Beckman, A.J. 1995. Recruitment Ecology and Reproductive Biology of the Puget Sound Rockfish, Sebastes emphaeus (Starks 1911). M.S. Thesis.

DeLacy, A.C., C.R. Hitz, and R.L. Dryfoos. 1964. "Maturation, gestation, and birth of rockfish (Sebastodes) from Washington and adjacent waters." Washington Department of Fisheries, Fisheries Research Papers 2:51-67.

Eisenhardt, E. 2001. "A marine preserve network in San Juan Channel: is it working for nearshore rocky reef fish?" Proceedings of the 2001 Puget Sound Research Conference. PSWQAT, Olympia, WA.

Chasco, B., L. Weis, and D. Cooper. 2000. "The Distribution and Densities of Larval Marine Protected Area Fishes in San Juan Channel." Friday Harbor Laboratories Course Papers, Marine Fish Ecology, Fish 499.

Jagielo, T.H. 1994. "Assessment of lingcod (Ophiodon elongatus) in the area north of 45o46'N (Cape Falcon) and south of 49o00'N in 1994." Appendix I. In: Status of the Pacific coast groundfish fishery through 1994 and recommended acceptable biological catches for 1995. Pacific Fishery Management Council. Portland, OR.

Martell, S., C. Walters, and S. Wallace. 2000. "The use of marine protected areas for the conservation of lingcod." Bulletin of Marine Science 66 (3): 957-990.

McCormick, M.I., and J.H. Choat. 1987. "Estimating total abundance of a large temperate-reef fish using visual strip-transects." Marine Biology 96: 469-478.

Moulton, L.L. 1977. An ecological analysis of fishes inhabiting the rocky nearshore regions of northern Puget Sound, Washington. Ph.D. Dissertation, University of Washington, Seattle.

Murray, M. 1998. "The Status of Marine Protected Areas in Puget Sound." Puget/Sound/Georgia Basin Environmental Report Series: Number 8. 2 Vols.

Paddack, M.J., and J.A. Estes. 2000. "Kelp forest fish populations in marine reserves and adjacent exploited areas of central California." Ecological Applications 10(3): 855-870.

Palsson, W.A. 1998. "Monitoring the response of rockfishes to protected areas." Pages 64-73 in M.M.Yoklavich,ed. Marine harvest refugia for West Coast rockfish: A workshop. NOAA- TM-NMFS-SWFC-255. La Jolla, CA.

Palsson, W.A., and others. 1997. 1995 Status of Puget Sound Bottomfish Stocks (revised). Washington Department of Fish and Wildlife Report MRD97-03.

Richards, L.J., and A.J. Cass. 1986. "The British Columbia inshore rockfish fishery: Stock assessment and fleet dynamics of an unrestricted fishery." In: Proceedings of the International Rockfish Symposium, Lowell Wakefield Fisheries Symposium. Anchorage, Alaska, USA, October 20-22, 1986. Alaska Sea Grant Report, No. 87-2, p 299-308.

Roberts, C.M., and N.V.C. Polunin. 1991. "Are marine reserves effective in management of reef fisheries?" Review of Fish Biology and Fisheries 1: 65-91.

Russ, G., and A. Alcala. 1997. "Do marine reserves export adult fish biomass? Evidence from Apo Island, Central Philippines." Marine Ecology Progress Series 132:1-9.

Washington, P.M., R. Gowan, and D.H. Ito. 1978. "A biological report on eight species of rockfish (Sebastes spp.) from Puget Sound, Washington." Northwest and Alaska Fisheries Center Processed Report, NOAA/NMFS, Reprint F.

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