Incorporating reef fish avoidance behavior improves accuracy of species distribution models

Species distribution models (SDMs) are used to interpret and map fish distributions based on habitat variables and other drivers. Reef fish avoidance behavior has been shown to vary in the presence of divers and is primarily driven by spearfishing pressure. Diver avoidance behavior or fish wariness may spatially influence counts and other descriptive measures of fish assemblages. Because fish assemblage metrics are response variables for SDMs, measures of fish wariness may be useful as predictors in SDMs of fishes targeted by spearfishing. We used a diver operated stereo-video system to conduct fish surveys and record minimum approach distance (MAD) of targeted reef fishes inside and outside of two marine reserves on the island of Oʻahu in the main Hawaiian Islands. By comparing MAD between sites and management types we tested the assumption that it provides a proxy for fish wariness related to spearfishing pressure. We then compared the accuracy of SDMs which included MAD as a predictor with SDMs that did not. Individual measures of MAD differed between sites though not management types. When included as a predictor, MAD averaged at the transect level greatly improved the accuracy of SDMs of targeted fish biomass.

Mesopelagic fish avoidance from the vessel dynamic positioning system

The study of marine organism behaviour and vertical distribution requires the use of techniques that do not disturb their natural state. This study analyses the mesopelagic fishes behaviour influenced by the presence of a research vessel. Acoustic data recorded on board the RV “Ángeles Alvariño” during the RAPROCAN 2017 survey showed a clear pattern of mesopelagic fishes migrating deeper in the water column at night when the DP system was connected. Details on how the scatterers changed their trajectory when migrating to the surface at night and the progressive increase in avoidance depth when dawn approached is shown. An experiment was carried out to discern fish reaction to vessel lights and to the DP system. While a dispersed diving was detected when the lights were switched on, a more acute reaction to the DP system was registered with not only vertical displacement, but also an increment in scattering produced by an aggregating behaviour. Both vessel DP-noise and light modify the mesopelagic fish behaviour, which needs to be accounted for when studying mesopelagic layers close to the surface. Surveys aiming at estimating abundance and biomass from these species are encouraged to do so at day time.

Changes in behavioural and locomotory activities of freshwater fish, Cirrhinus mrigala (Hamilton) in response to sublethal exposure of Chlorpyrifos

The aim of the present study was to analyze the impact of sub-lethal toxicity of chlorpyrifos, one of the largest market selling agrochemical on physiological parameters of teleost fish, Cirrhinus mrigala addressing the possible causative involvement in behavioural and locomotion responses. Primarily, the acute toxicity (96h LC50) test was carried out and the value calculated by probit analysis was found to be 0.44 mg L-1. Further, one-fifth, one-tenth and one-twentieth of 96 h LC50 were selected as sublethal concentrations for sub acute studies. The experiment was carried out for 21 days and the alternative behaviour was recorded in terms of Air Ingulping (AI), Operculum Beat Frequency (OBF), Surfacing Movement (SM), Vertical Hanging (VH) and Tail Beat Frequency (TBF) on duration day 2, 4, 7, 14 and 21. Significant effect of both the concentrations and duration was observed in fishes treated with selected doses of chlorpyrifos. It was found that AI, OBF, SM, VH, TBF was highest on day 7 at 0.08 mg L-1 concentration of Chlorpyrifos. The findings revealed that there is a need to control the use of chlorpyrifos because of its toxicity. All the fish avoidance tests proved to be an important predictive and sensitive biomarker in aquatic monitoring and pollution management.