Measurements of Spillover Fish Naiveté from Marine Reserves May Help Support Marine Conservation and Improve Models of Spillover

Although human induced changes in fish behavior may affect fisheries and marine sanctuaries, the science is lacking. Januchowski-Hartley et al. (2012) conducted an experiment in the Philippines using the fish flight initiation distance (FID) to measure the naiveté of three genera of fishes.  Data were collected within borders of three marine reserves, outside three marine reserves and in three controlled fishing areas. Although it is accepted that marine biomass spillover from reserves exists, data on human-induced behavioral changes are scarce, and are needed to understand fishery success. Recent diffusion models predicting fish abundance across boundaries of reserves assume that fishes do not vary in catchability as they move from the reserve to unprotected areas but Januchowski-Hartley et al. found that FID remains high for some distance outside reserve borders, meaning that spillover of fish naiveté towards spear fishers occurs. Evelyn Byer
Januchowski‐Hartley, F.A., Graham, N.A.J., Cinner, J.E., Russ, G.R., 2012. Spillover of fish naïveté from marine reserves. Ecology Letters 16, 191–197.

Januchowski‐Hartley et al. measured the FID and biomass of three different genera of tropical reef fishes in the Phillipines. Acanthuridae and Scaridae are two key families targeted by local fishereies, while species in the control family, Chaetodontidae, are small and not targeted by spear fishers. FID and biomass were surveyed from 200 m inside to 200 m outside one boundary of each of three marine reserves: Apo Island, Tandyang, and Tubod. Fish FID was estimated by a diver on snorkel imitating spearfisher behavior. When the fish fled, a marker was dropped on the substrate under the diver’s head, and directly below the fishes pre-fleeing location. The distance between the two markers was immediately measured with a tape measure. Biomass and abundance were estimated by a free diver at nine different distances from the boundary at each area.
Both fishes targeted by spearfishers, Acanthuridae and Scaridae, showed linear or weakly exponential increases in FID across marine reserve boundaries. This means that within reserves, spearfishers were able to swim closer to the fish before they fled than outside the park boundary. This demonstrates the spillover of naiveté from within marine reserves to surrounding fished areas and suggests that the export of naïve behavior may be a general benefit to spearfishers of marine reserves. While there was a significant difference between distance and FID for the fish families targeted by fisheries, the untargeted fish family Chaetodontidae showed no significant change in FID across reserve boundary suggesting that this change in FID is influenced by fishing. None of the sampled families showed trends at any control fished boundary meaning this trend is unique to marine reserves. Both target families displayed a higher biomass inside reserves than in fishing grounds adjacent to reserves. Surprisingly, the biomass adjacent to reserves was lower than biomass in control fished areas suggesting that this decrease in biomass is consistent with ‘fishing the line’ behavior; increased fishing pressure directly outside marine reserve borders. Januchowski‐Hartley et al. suggests that the lack of biomass across marine reserve borders may be exacerbated by naïve fishes with lower FID being more easily caught. Increased FID outside of park boundaries may be facilitated with direct experience of a non-fatal encounter with spearfisher, or indirectly through linking the visual image of a predator with chemical alarm cues with more exposures resulting in larger effects. Also, an increase in FID outside park boundaries could result from the selective removal on naïve fishes by spearfishers. These finding are relevant because they add a new factor to marine reserve models which may be overestimating increases in biomass and may increase stake-holder support for marine reserves.

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