Deploy fishing gear at selected times (day/night) to avoid unwanted species
Overall effectiveness category Awaiting assessment
Number of studies: 2
Background information and definitions
Many marine species undertake daily vertical migrations through the water column during day/night cycles, influenced by factors such as temperature, light levels, and prey availability. Some shark species, for example, swim closer to the sea surface at night than during the day (Bromhead et al. 2012). There is also evidence that in sufficient levels of light some fish are better able to detect, and thus better avoid, approaching trawl gear (Glass & Wardle 1989) or escape from parts of the net after entering it (Gabr et al. 2007). The timing of setting and hauling gear can, therefore, affect catch rates (Gilman et al. 2008), so fishing at a specific time of day/night may help to avoid unwanted or threatened fish species whose distribution or behaviour decreases the likelihood of capture.
Evidence for similar interventions is summarized under ‘Deployment of fishing gear and mode of operation - Deploy fishing gear at selected depths to avoid unwanted species’ and ‘Selectively avoid unwanted fish based on temperature distribution’.
Bromhead D., Clarke S., Hoyle S., Muller B., Sharples P. & Harley S. (2012) Identification of factors influencing shark catch and mortality in the Marshall Islands tuna longline fishery and management implications. Journal of Fish Biology, 80, 1870–1894.
Gabr M., Fujimori Y., Shimizu S. & Miura T. (2007) Behaviour analysis of undersized fish escaping through square meshes and separating grids in simulated trawling experiment. Fisheries Research, 85, 112–121.
Gilman E., Clarke S., Brothers N., Alfaro-Shigueto J., Mandelman J., Mangel J., Petersen S., Piovano S., Thomson N., Dalzell P., Donoso M., Goren M. & Werner T. (2008) Shark interactions in pelagic longline fisheries. Marine Policy, 32, 1–18.
Glass C.W. & Wardle C.S. (1989) Comparison of the reactions of fish to a trawl gear, at high and low light intensities. Fisheries Research, 7, 249–266.
Supporting evidence from individual studies
A replicated, controlled study in 2014 at an estuary/lagoon site in Lake Wooloweyah, Australia (Broadhurst et al. 2015) found that trawling for prawns during the day decreased the number, but not weight, of unwanted fish overall compared to the usual practice of trawling during the night, and the effect varied between species. Overall catch rate of unwanted fish by number was lower during the day compared to the night (day: 57–72 fish/ha, night: 107–109 fish/ha), but by weight catch rate was the same (both 1 kg/ha). Trawl deployments during the day reduced the catches of three of seven individual fish species (day: 2–7 fish/ha, night: 5–34 fish/ha), but catch rates were higher than at night for three others (day: 2–65, night: <1–35 fish/ha) and the same for one (2 fish/ha). See original paper for individual species data. Number and weight of commercial target school prawns Metapenaeus macleaya were the same for both night and day deployments (number: 3,272–3,958 prawn/ha, weight: 7–9 kg/ha). In March and April 2014, identical trawl nets were compared by trawling for 45 minutes during six days and four nights. Two types of lengths with different wing and body tapers were tested during 44 paired deployments.Study and other actions tested
A replicated, controlled study (year not stated) of two seamount marine reserves in the South Pacific Ocean 200 km off New South Wales, Australia (Williams et al. 2016) found that selective fishing at specific times and depths avoided the unwanted catch of Harisson’s dogfish Centrophorus harrissoni in a restricted commercial blue-eye trevalla Hyperoglyphe antarctica handline fishery. Across areas, catch rates were lower (0 fish/100 hooks) during the day at seamounts 280–550 m deep (defined as being ‘non-dogfish habitat’), but not at the deeper seamounts (0.4 fish/100 hooks), compared to seamounts at 280–550 m during the night (0.1 fish/100 hooks), both of the latter defined as ‘dogfish habitat’. Catches of trevalla were highly variable but appeared slightly lower in the ‘non-dogfish’ habitat’ compared to the ‘dogfish habitat’ (non-dogfish: 8.2–34.3 fish/100 hooks, dogfish: 9.1–48.9 fish/100 hooks; data not tested for significance). Hydraulically powered handlines with 18 hooks each were deployed during 10 vessel trips 4-5 days long during the day in mid-water (depths) and deep-water (depths), and at night in mid-water. In ‘other habitat’ 1,036 handline deployments were carried out and 407 in ‘dogfish habitat’. Handlines were deployed at randomly selected positions and hauled after 5-10 minutes or until it was felt several fish had been hooked. Details of when the study took place were not provided. Fish were identified and counted.Study and other actions tested