Fish behavior is intimately linked to fishing catchability. Measurements of fish behavior may provide quantitative indicators that inform about the impact of fishing pressure and help design effective management strategies. The implications of spearfishing pressure on fish behavior have been mainly characterized using single quantitative indicators such as flight initiation distance (FID), which provide incomplete views of spearfisher-fish behavioral interactions. We used an integrative approach to advance the understanding of spearfisher-fish behavioral interactions by complementing FID estimates with post-flight responses (i.e., individual fish behavior after fleeing), and the decreasing probability to catch a fish at increasing distance from a speargun. We first collected empirical observations of white seabream (Diplodus sargus) FID and post-flight behavior in response to an approaching human (spearfisher or snorkeler) inside and outside marine protected areas. We then combined these observations with simulations based on an innovative model representing how catchability changes during a spearfisher-fish behavioral interaction. Empirical results showed that the likelihood of a still-vulnerable post-flight response after fleeing was inversely related to increasing exposure to spearfishers. This demonstrates that post-flight response can be used as an indicator of spearfishing pressure. Moreover, post-flight responses provided complementary information to that provided by FID, suggesting that these two indicators should be integrated for a holistic view of spearfishing-fish interactions, such as in the model and simulations presented here. The simulations demonstrated that: (i) accounting for post-flight responses may increase likelihood of approach by spearfisher within speargun range by up to 20%; and (ii) accounting for post-flight responses and decreasing probability of capture with increased distance from speargun drastically reduces estimates of likelihood of capture of white seabream at minimum catch length limit outside marine protected areas compared with using FID as single indicator of catchability. Synthesis and applications: First, integrating FID measurement with post-flight responses provides a more realistic indicator to measure fish behavioral reaction to spearfishing pressure. Second, the model presented here showed that spearfishing mortality may drastically decrease when accounting for both prey behavior (i.e., FID and post-flight responses) and spearfishers effectiveness (i.e., probability to catch a fish at increasing distance from a speargun). This must be considered to understand population dynamics and potential changes in catchability when spearfishing is managed through temporal restrictions (e.g., seasonal or periodic closures).

Measurement of flight-initiation distance, post-flight behavior and estimated size of the fish were collected during underwater observations We measured FID and post-flight behavioral response to four treatments: two areas with different levels of harvesting protection status (protected/unprotected from spearfishing) and two diver configurations (potentially threatening spearfishing with a speargun and non-threatening snorkeling without a speargun). All observations were conducted at a minimum distance of 750 m from the borders of marine protected areas. All sites were surveyed by the same operator. The spearfisher was equipped with a speargun (100 cm long, slings were removed and substituted with PVC tubes to not violate regulations of the MPAs) and with the typical spearfishing equipment (black wetsuit, long black fins and black mask). The snorkeler equipment consisted of a short blue wetsuit, short blue fins and a colored mask. The different diver configurations (spearfisher/snorkeler) were applied inside and outside each marine protected area in a random order over 4–7 consecutive days. Success of approach and capture can be obtained by running the model associated with the data. The model represents a spearfisher-fish behavioral interaction to assess how likelihood of approach and capture a white seabream changed when accounting for: (i) FID; (ii) post flight behavior; and (iii) the decreasing probability to catch a fish at increasing distance from a speargun. To create models for (i) and (ii) we used the empirical data described above where the observer simulated a spearfisher approach both inside and outside marine protected areas, while for (iii), we also interviewed 16 specialized spearfishers and asked them to estimate the probability (0-100%) to successfully catch a medium size D. sargus (i.e., 30-35 cm) by shooting with a 100 cm long speargun from four distances (2.5; 3.0, 3.5; 4.0 m).

Funding provided by: Spanish Ministry of Science and InnovationCrossref Funder Registry ID: http://dx.doi.org/10.13039/501100004837Award Number: RYC2021-033065-I