Growth parameter k and location affect body size responses to spatial protection by exploited rockfishes

Abstract

For many fish taxa, trophic position and relative fecundity increase with body size, yet fisheries remove the largest individuals, altering food webs and reducing population productivity. Marine reserves and other forms of spatial protection can help mitigate this problem, but the effectiveness of these management tools may vary interspecifically and spatially. Using visual survey data collected on the Central Coast of British Columbia, for 12 species of exploited rockfish we found that body size responses to spatial fishery closures depended on interspecific variation in growth parameter k (the rate at which the asymptotic body size is approached) and on location. For two closures, relative body sizes were larger at protected than at adjacent fished sites, and these differences were greater for species with lower k values. Reduced fishery mortality likely drove these results, as an unfished species did not respond to spatial protection. For three closures, however, body sizes did not differ between protected and adjacent fished sites, and for another closure species with higher k values were larger at fished than at protected sites while species with lower k values had similar sizes in both treatments. Variation in the age of closures is unlikely to have influenced results, as most data were collected when closures were 13 to 15-years-old. Rather, the lack of larger fish inside four of six spatial fishery closures potentially reflects a combination of smaller size of the area protected, poor fisher compliance, and lower oceanographic productivity. Interspecific differences in movement behavior did not affect body size responses to spatial protection. To improve understanding, additional research should be conducted at deeper depths encompassing the distribution of older, larger fish. Our study—which was conceptualized and executed by an alliance of Indigenous peoples seeking to restore rockfishes—illustrates how life history and behavioral theory provide a useful lens for framing and interpreting species differences in responses to spatial protection.

Hotspots for rockfishes, structural corals, and large-bodied sponges along the central coast of Pacific Canada

“…depth of dive surveys. Consistent with earlier publications 33 , analyses excluded fish < 10 cm-long. Sponge cover categories: 0 = 0%; 1 = 1- 25%; 2 = 26–50%; 3 = 51–75%; 4 = 76–100% Mid-depth video transects 32 , 50 , 51 2015–2018 15–200 (67) Belt transects of variable size were divided into bins covering 75–130 m 2 (mean = 116 m 2 ) to reduce depth and habitat variability within spatial units.…”

Hotspots for rockfishes, structural corals, and large-bodied sponges along the central coast of Pacific Canada

“…Data were collected by four fishery-independent methods-shallow diver transects, mid-depth video transects, deep video transects, and hook-and-line sampling-detailed in earlier publications [30][31][32][33]47,48 (Table 1). Throughout the sampling period (2006)(2007)(2013)(2014)(2015)(2016)(2017)(2018)(2019)(2020): Table 1), we focused on the geographic expansion of sampling locations, rather than on tracking temporal variability within sites.…”

“…1) and are among the Indigenous governance partners for the MPA network. Collaborating under the umbrella of the Central Coast Indigenous Resource Alliance (CCIRA), since 2013 they have been using fishery-independent methods (dive and towed video transects, hook and line sampling) to survey biodiversity features in their territories [30][31][32] . The surveys encompass oceanic and inland waters at depths of 5 m to 200 m. Additionally, research in 2018 included a collaboration with Fisheries and Oceans Canada (DFO: the federal aquatic ecosystem and resource management agency)-which contributed technical capacity and infrastructure (large vessel, crew, and the towed video camera described by Gale et al 33 ) to sample depths of 200 m to 500 m.…”

Protecting our coast for everyone's future: Indigenous and scientific knowledge support marine spatial protections proposed by Central Coast First Nations in Pacific Canada

“…Also, research within the NSB points to differences between protected and fished areas in the trophic structure of rockfishes and lingcod (Olson et al, 2019). MPA benefits for rockfish, however, may require many years to accrue and the required time may vary between species and locations (McGreer et al, 2020; Starr et al, 2015).…”