Effects of diel period and diurnal cloud cover on the species selection of short and long penaeid trawls

Published source details Broadhurst M.K., Sterling D.J. & Millar R.B. (2015) Effects of diel period and diurnal cloud cover on the species selection of short and long penaeid trawls. Fisheries Research, 170, 144-151.
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This study is summarised as evidence for the following.

	Action	Category
	Deploy fishing gear at selected times (day/night) to avoid unwanted species Action Link
	Modify the design or configuration of trawl gear (mixed measures) Action Link

Deploy fishing gear at selected times (day/night) to avoid unwanted species

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.

(Summarised by: Khatija Alliji)
Modify the design or configuration of trawl gear (mixed measures)

A replicated, paired study in 2014 of an area of shallow sandy mud bottom in an estuary lagoon site in off the Tasman Sea, Australia (Broadhurst et al. 2015) found that modifying the design of prawn trawls (body length/side taper) reduced the unwanted catch of only one of seven main fish species caught, and for most of the rest, catches varied with light conditions (day/night). Catch rate of only one of seven unwanted fish species, Australian anchovy Engraulis australis, was lower in a short trawl (0–2 fish/ha) than a long trawl (1–3 fish/ha), irrespective of day or night sampling times, and southern herring Herklotsichthys castelnaui catch rate was lower in the short trawl during daylight only (short: 48 fish/ha, long: 68 fish/ha). However, regardless of trawl type, catch rates of forktail catfish Arius graeffei, pinkbreast siphonfish Siphamia roseigaster, and yellowfin bream Acanthopagrus australis, were lower during the day than night, whereas whitebait Hyperlophus vittatus catches were lower during the night. Neither trawl type nor sampling time affected catch rates of Ramsey's perchlet Ambassis marianus (see original paper for species individual data by trawl type/sampling time). In addition, the catch rates (weight and numbers) of the target species school prawns Metapenaeus macleayi were lower in the short trawl than the long trawl (short: 7 kg/ha, long: 9 kg/ha). In March and April 2014, a total of 44 paired deployments (45 min) were made in Lake Wooloweyah, Clarence River estuary, New South Wales, with one short and one long prawn trawl, during six days and four nights. Trawls nets were identical apart from different configurations of wing and body tapers (see original paper for gear specifications).

(Summarised by: Khatija Alliji)