Analysis of fish population size distributions confirms cessation of fishing in marine protected areas

Abstract

The number of protected areas that restrict or prohibit harvest of wild populations is growing. In general, protected areas are expected to increase the abundance of previously-harvested species. Whether a protected area achieves this expectation is typically evaluated by assessing trends in abundance after implementation. However, the underlying assumption that harvest has actually ceased is rarely tested directly. Determining whether illegal harvest (poaching) has continued in a protected area is important to planning enforcement and adaptive management. Here, we estimated harvest rates for four kelp forest fish species inside marine protected areas (MPAs) and non-MPA reference sites in the California Channel Islands, from 2003 (when MPAs were implemented) to 2017. We estimated harvest by fitting a size-structured population model to survey data. Overall, harvest rates were effectively zero in MPAs but much higher in non-MPA sites. This indicates successful adherence to MPA regulations, and possible displacement of fishing effort to reference sites. However, some poaching was detected in two MPA sites, highlighting the importance of assessing this quantity. This modeling approach could provide a tool to complement the long-term management of MPA networks, particularly given the difficulty of acquiring harvest rate data at the spatial scale of individual MPAs.

Sea urchin harvest inside marine protected areas: an opportunity to investigate the effects of exploitation where trophic upgrading is achieved

“…Therefore, appropriate conservation measures are needed to contrast unsustainable harvesting, especially where other restrictions are been taken to achieve trophic upgrading. This would be in agreement with the general concern of stakeholders, since MPAs are known to achieve habitat conservation via halting fish harvest, rather than contributing to the further depletion of the stock ( White et al., 2021 ) and changing the restricted harvest zones to no harvest has been widely discussed within the marine literature ( Murray et al, 1999 ; Abecasis, Afonso & Erzini, 2015 ).…”

Assessing the population‐level conservation effects of marine protected areas

“…We found a similar increasing trend in the response ratios of targeted species (Figure 3). This provides evidence that the Channel Islands MPAs are large enough and sufficiently well-enforced as to provide meaningful protection within their borders (White et al, 2020). These response ratios cannot, however, be used as a definitive indicator of population-level effects of these MPAs.…”

Increasing spillover enhances southern California spiny lobster catch along marine reserve borders

“…Such a scenario is possible when lobster abundance and catch were relatively high before reserves were implemented (Halpern et al, 2009; Hilborn et al, 2004). Additionally, the fishery may not actively fish reserve borders if there is not suitable habitat along reserve borders (Freeman et al, 2009; Guenther et al, 2015; White et al, 2020; ). The response of recovering species inside reserves can also be long and transient (White et al, 2013).…”