Performance of Bycatch Reduction Devices in the Small-Scale Shrimp Trawl Fishery of the Persian Gulf

<em>Abstract.</em>—We examined the swimming performance and behavior of red snapper, <em>Lutjanus campechanus. </em>Our intention was to use this information toward developing a more efficient bycatch reduction device for use in the Gulf of Mexico shrimp trawl fishery. Using a Brett type swim tunnel, we found a significant effect of fish size and season on red snapper critical swimming speeds. For fish ranging between 6 and 17 cm standard length, critical swimming speeds ranged from about 35–70 cm/s, depending upon season. However, critical swimming speeds did not differ between day and night. This was an important observation since the majority of shrimp trawling in the Gulf occurs at night. We constructed and tested in the laboratory, a Vortex Generating Bycatch Reduction Device (VGBRD) that may prove useful in the shrimp trawl fishery. During behavioral tests during daylight, 79.2% of red snapper exited the VGBRD in an average of 4.1 min. However, during night-time tests, only 17.6% of red snapper exited the VGBRD in an average of 5.0 min. Behavioral tests revealed a strong negative phototactic response in dark adapted red snapper. We found that, during night-time tests when the VGBRD was illuminated with LED lights placed downstream of the exit, 96% of red snapper exited the device in 7.1 min. In color/ contrast choice experiments, red snapper unerringly associated with the dark colored (black or dark green) panel placed on the bottom of the experimental tank. In another set of experiments, we found that snapper displayed a strong optomotor response, i.e. the tendency to following and match speeds with a moving pattern. Illumination, color/contrast, and/or the optomotor response may improve bycatch reduction device performance.

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Investigation of Atmospheric Conditions Associated with a Storm Surge in the South-West of Iran

10.20944/preprints202108.0517.v1 ◽

2021 ◽

Author(s):

Esmaeil Abbasi ◽

Hana Etemadi ◽

Joseph Smoak ◽

Iman Rousta ◽

Haraldur Olafsson ◽

...

Keyword(s):

Storm Surge ◽

Persian Gulf ◽

High Tide ◽

Wrf Model ◽

Specific Humidity ◽

Small Scale ◽

Atmospheric Conditions ◽

Severe Thunderstorms ◽

Meridional Winds ◽

The Persian Gulf

Severe thunderstorms are often accompanied by strong vertical air currents, temporary wind gusts, and heavy rainfall. The development of this atmospheric phenomenon over tropical shallow water zones, such as bays, can lead to intensification of atmospheric disturbances and produce a small-scale storm surge. Here, the storm surge that occurred on 19 March 2017 in the Persian Gulf coastal area has been investigated. Air temperature, precipitation, mean sea level pressure, wave height, wind direction, wind speed, geopotential height, zonal components, meridional winds, vertical velocity, relative humidity, and specific humidity obtained from the European Centre for Medium-Range Weather Forecasts (ECMWF (and Global Forecast System (FNL) were used to implement the Weather Research and Forecasting (WRF) model. The results showed that the main cause of the storm surge was the occurrence of a supercell thunderstorm over the Persian Gulf. The formation of this destructive phenomenon resulted from a downburst under Cumulonimbus cloud and high-velocity air subsidence, after collision with the sea surface coinciding with the high tide. This caused a severe, yet temporary, gust, which in turn caused the creation of the four waves of 3.1 m height along the coast of Bandar Dayyer.

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A Case Study of Sampling Strategies for Estimating the Length Composition of Commercial Catches: The Sri Lankan Shrimp Trawl Fishery

Crustaceana ◽

10.1163/156854011x607024 ◽

2011 ◽

Vol 84 (12-13) ◽

pp. 1581-1591 ◽

Cited By ~ 3

Author(s):

Gunnar Stefánsson ◽

M. D. S. T. De Croos

Keyword(s):

Survey Design ◽

Total Variance ◽

Sampling Scheme ◽

Small Scale ◽

Sampling Variance ◽

Length Frequency ◽

Commercial Catch ◽

Frequency Distributions ◽

Trawl Fishery ◽

Shrimp Trawl

AbstractScientific surveys are expensive and often not feasible for artisanal and small-scale fisheries. Biological samples from the commercial catch are the principal source of information in monitoring these fisheries. A pilot sampling scheme of commercial craft conducted during a four-month period on the artisanal coastal shrimp trawl fishery in Sri Lanka revealed that the length compositions of two short-lived shrimp species (Metapenaeus dobsoni and Parapenaeopsis coromandelica), derived from commercial catches, showed high sampling variance and thus resulted in considerable noise in the length-frequency distributions. An analysis of variance components revealed that the total variance was mainly governed by the variance due to the number of samples. Hence, a more effective survey design was to collect samples from as many fishing craft as possible rather than increasing the sample size. The observed total variance of 0.4 based on measuring 43 109 individuals of M. dobsoni from 4 boats per sampling day (∼300 individuals/sample) in the pilot sampling was revised with the new sampling scheme, which reduced the variance to 0.2 based on measuring only 28 800 individuals from 6 boats per sampling day (∼150 individuals/sample). The length-frequency distributions constructed with the revised sampling scheme resulted in less noise in the monthly progression of modes.

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