Summary of Findings from Periodic Scuba Surveys of Bottomfish Conducted Over a Sixteen-Year Period at Six Nearshore Sites in Central Puget Sound

When only results from short-term monitoring programs are available it can be difficult for resource managers to gauge the effects of regulatory actions aimed at long-term resource conservation. This is particularly true for species that are long-lived, slow-growing, and late to mature. For these species, demographic changes in response to management actions may be slow to manifest and difficult, or impossible, to detect over time spans of fewer than two generations. Data obtained from long-term monitoring is more likely to capture changes over time in fish communities composed of a wide variety of life spans and other life history attributes.

This report summarizes the data from sixteen years of bottomfish surveys via scuba at six central Puget Sound sites. We examined the data for long-term changes or trends in abundance, size, and distribution of several key bottomfish species. Further, we make comparisons among and between those sites surveyed that fall within marine protected areas (MPAs) and those that do not. In order to gain added perspective from our survey data, we compared our data to those acquired from four different scuba-based studies conducted prior to the commencement of our surveys at four of our sites.

At all six sites, species composition was dominated by just three taxonomic groups: rockfishes, surf perches, and greenlings, though the relative proportions of those groups varied among sites. Species richness also varied within and among groups, and within and among sties. Curiously, the greatest number of species observed was at the most heavily fished site, while the fewest number observed was at the most protected MPA. In pairwise comparisons of species composition by season (spring and fall), nearly all were significantly different both within and between sites. Though not confirmed, the data suggest that differences in species composition may occur along a latitudinal gradient. The species that contributed most to the differences between sites were Striped Seaperch, Puget Sound Rockfish, and Brown Rockfish.

At most sites, there was evidence of strong juvenile rockfish recruitment in 2006/07 for one or more of the following species: Black Rockfish, Quillback Rockfish, and Copper Rockfish. This event was made apparent by relatively high density "pulses" in length classes over time, whereby, unusually high numbers of juvenile fish enter a population and, with growth, sequentially moved from smaller to larger length-classes over time (i.e., a detectable "pulse" in length-class frequency was detected over time.)

Some have suggested that Lingcod, a high trophic-level feeder, may exert predatory top-down control over some rockfish species. We examined our data from the site where overall rockfish and lingcod density was greatest, and where the highest density of Puget Sound Rockfish occurred. Puget Sound Rockfish rarely exceed 20 cm in length and bear fewer and less robust spines than many other rockfish species, thus they are more vulnerable to predation than larger rockfishes. We searched for inverse relationships between Lingcod and rockfish density and biomass (e.g., increasing trends in Lingcod density accompanied by decreasing trends in rockfish density). Such relationships could provide evidence that Lingcod predation is a factor in limiting rockfish population growth. A strong relationship between Lingcod and rockfish density and biomass was not apparent.

The frequencies of occurrence of Lingcod and rockfish in the largest length-classes were greatest at the Bracket's Landing Shoreline Conservation Area, the most longstanding MPA in Puget Sound. However, a substantial downward trend in the density of Copper and Quillback Rockfish in the largest length classes was apparent during the first seven years of the survey period. We considered multiple explanations and reasoned that senescence is the most likely explanation, though poaching may be a contributing factor. Some rockfish populations are known to be dominated by a small number of year classes. Given the age and long-term protection status of fish at Bracket's Landing, we hypothesize that a strong cohort of Copper and Quillback Rockfish reached terminal age and perished over the course of several years. The occasional occurrence of large dead Lingcod and rockfish at Bracket's Landing lends some support to this hypothesis. No dead Lingcod or rockfish were encountered at any of the other surveyed sites.

We compared our findings to studies that were conducted at four of our sites during years prior to our surveys. One of the most striking contrasts was the complete absence of Lingcod noted at Bracket's Landing during surveys conducted in 1975/76. In our surveys, Lingcod frequency of occurrence at Bracket's Landing was 100%. Furthermore, the annual mean lengths for Lingcod were greater at Bracket's Landing than at any other site we surveyed. All four of the comparable studies indicate changes over time in rockfish species composition.

Our survey results provide an informative perspective on the recent status of several key bottomfish species at six nearshore sites in central Puget Sound and will serve as an important benchmark for future surveys. However, our ability to identify and interpret trends over time, particularly for rockfishes, was confounded by factors such as high interannual variability in juvenile recruitment, poorly understood post recruitment inter- and intraspecific interactions, and, at some sites, discontinuous sampling and changes in protection statuses. In comparing MPA sites to non-MPA sites, we were not able to discern any trends that could be unequivocally linked to harvest management actions, though at least two observations suggest evidence of a protection response. First, at the Orchard Rocks Conservation Area, subsequent to the year (1998) that it was afforded MPA status, a persistent increase in rockfish density and biomass occurred. And second, the mean length, density, and biomass of Lingcod at the Keystone Conservation Area increased after the year (2002) that it was afforded MPA protection. Unlike rockfishes, which typically grow at substantially slower rates in Puget Sound, Lingcod grow rapidly, particularly during the first several years of their life. The rapid growth, and accompanying rapid increase in fecundity, of Lingcod makes it a potentially valuable first-response species for detecting positive effects of conservation efforts.

We recommend that the surveys be resumed at an interval coinciding approximately with two elapsed generations for key species and, based on our findings here, we conclude with several recommendations for research and management improvements moving forward.