Supply–demand equilibria and the size–number trade‐off in spatially structured recreational fisheries

Abstract

Recreational fishing effort varies across complex inland landscapes (e.g., lake-districts) and appears influenced by both angler preferences and qualities of the fishery resource, like fish size and abundance. However, fish size and abundance have an ecological trade-off within a population, thereby structuring equal-quality isopleths expressing this trade-off across the fishing landscape. Since expressed preferences of recreational anglers (i.e., site-selection of high-quality fishing opportunities among many lakes) can be analogous to optimal foraging strategies of natural predators, adopting such concepts can aid in understanding scale-dependence in fish-angler interactions and impacts of fishing across broad landscapes. Here, we assumed a fish supply-angler demand equilibria and adapted a novel bivariate measure of fishing quality based on fish size and catch rates to assess how recreational anglers influence fishing quality among a complex inland landscape. We then applied this metric to evaluate (1) angler preferences for caught and released fish compared to harvested fish, (2) the nonlinear size-numbers trade-off with uncertainty in both traits, and (3) the spatial-scale of the equilibria across 62 lakes and four independent management regions in British Columbia's (BC) rainbow trout Oncorhynchus mykiss fishery. We found anglers had low preference for caught and released fish (~10% of the value compared to harvested fish), which modified anglers' perception of fishing quality. Hence, fishing quality and angler effort was not influenced simply by total fish caught, but largely by harvested fish catch rates. Fishing quality varied from BC's northern regions (larger fish and more abundant) compared to southern regions (smaller fish and less abundant) directly associated with a 2.5 times increase in annual fishing effort in southern regions, suggesting that latent fishing pressure can structure the size-numbers trade-off in rainbow trout populations. The presence of two different equal-quality isopleths suggests at least two effective landscapes support co-occurring ideal free distributions of recreational fishing effort in BC's rainbow fishery. Anglers' expressed preferences among lakes interacted with density dependent growth and survival within lakes to structure a size-numbers trade-off influencing how anglers perceive fishing quality and, ultimately, distribute across complex inland landscapes.

Interaction of ecological and angler processes: experimental stocking in an open access, spatially structured fishery

“…) with significantly different communities of anglers (Ward et al. , Wilson et al., in press). The northern region is characterized by low human population density, and lakes in this region are relatively distant from the largest urban centers in the province (i.e., Vancouver and surrounding municipalities).…”

“…) or to aggregate measures of fishing quality incorporating both fish abundance and fish size (Post et al. , Post and Parkinson , Wilson et al., in press), as well as non‐catch attributes (such as accessibility and crowding) and angler utility functions (Arlinghaus et al. ).…”

“…Our experimental approach, with controls, involved the manipulation of stocking rate in a subset of lakes after a period of unchanged stocking and replication of this manipulation in two pre‐defined regions known to differ substantially in latent fishing effort (i.e., the total population of anglers), driving distance to the biggest angler population in the province (in the Fraser River Valley, including Vancouver), and the average anglers’ perception of fishing quality (Wilson et al., in press). We hypothesized that a dynamic angler effort response to variation in fish abundance and size, created through manipulation of stocking rates, would result in spatial heterogeneity in angler effort across lakes with equivalent accessibility within a region.…”

“…). We used an empirically derived relationship between fish abundance and fish size across rainbow trout populations in BC (Wilson et al., in press) to provide a measure of catch‐related fishing quality that accounts for the size–abundance trade‐off in this system, and is expected to contribute, to some degree, to overall patch utility (Fig. ).…”

Synchrony — An emergent property of recreational fisheries

“…Outlining specific management goals and understanding the best way to implement a desirable change, while considering subsequent cascading consequences through space and time, will be necessary for successful management of these social‐ecological systems. Traditional recreational fisheries management techniques applied to the waterbody level, such as designated fishing seasons, species‐specific size and length limits, and fish stockings could also be balanced by taking a watershed‐scale approach (Mee et al., ; Nguyen et al., ; Wilson et al., ). We suggest that cross‐scale management that includes an understanding of how angler and resource heterogeneity interact through space and time will be most effective for maximizing ecosystem services within these recreational fisheries (Arlinghaus et al., ; Ward et al., ).…”