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. 2018 Dec 14;8(1):17876.
doi: 10.1038/s41598-018-35804-7.

Trawl Ban in a Heavily Exploited Marine Environment: Responses in Population Dynamics of Four Stomatopod Species

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Free PMC article

Trawl Ban in a Heavily Exploited Marine Environment: Responses in Population Dynamics of Four Stomatopod Species

Lily S R Tao et al. Sci Rep. .
Free PMC article

Abstract

Intensive trawling activities in Hong Kong waters have seriously depleted fishery resources and damaged marine benthic habitats over the last four decades. To minimize further destruction and rehabilitate fishery resources, the Hong Kong Government implemented a permanent territory-wide trawling closure on 31 December 2012. Such a trawl ban creates a unique opportunity to investigate recoveries in ecosystem structure and function following a major shift in disturbance regime by removing impacts from a major gear. This study was designed to test the hypothesis that dominant predatory mantis shrimps, including Harpiosquilla harpax, Miyakella nepa, Oratosquillina interrupta, and Oratosquilla oratoria would show signs of recovery following the trawl ban. Their population dynamics were investigated before and after the trawl ban. The results showed that their mean weight, mean carapace length and proportion of large-sized individuals increased significantly 3.5 years after the trawl ban, whilst their abundance, biomass and maximum length remained unchanged. This study suggests that the stomatopod assemblage in the human-dominated Hong Kong waters shows some initial signs of possible recovery following the trawl ban but also highlights the complexity of implementing fishery management and detecting changes resulted from management measures in a heavily urbanized seascape where many biotic and abiotic factors can influence their population dynamics.

Conflict of interest statement

The authors declare no competing interests.

Figures

Figure 1
Figure 1
(a) Monthly abundance (mean + SE; individuals/km2) and (b) biomass (mean + SE; kg/km2) of four stomatopod species collected in the western waters of Hong Kong from January 2004 to December 2004 (2004; before the trawl ban), June 2013 to May 2014 (2013–2014; immediately after the trawl ban), and June 2015 to May 2016 (2015–2016; 3.5 years after the trawl ban). HH: Harpiosquilla harpax, MN: Miyakella nepa, OI: Oratosquillina interrupta, OO: Oratosquilla oratoria.
Figure 2
Figure 2
(a) Monthly abundance (mean + SE; individuals/km2), (b) biomass (mean + SE; kg/km2) for carnivorous crabs (C), four stomatopod species (MS), total carnivorous crustaceans (C + MS) and predatory fishes (PF), and (c) relative abundance and biomass of four stomatopod species over total carnivorous crustacean collected in the western waters of Hong Kong from January 2004 to December 2004 (2004; before the trawl ban) and June 2013 to May 2014 (2013–2014; immediately after the trawl ban) and June 2015 to May 2016 (2015–2016; 3.5 years after the trawl ban). Significant differences are indicated by asterisks: *p < 0.05; **p < 0.01, ***p < 0.001.
Figure 3
Figure 3
(a) Mean weight (mean + SE; g/individual), (b) mean carapace length (mean + SE; cm/individual), and (c) L95% (mean + SE; cm) of the four stomatopod species collected in the western waters of Hong Kong from January 2004 to December 2004 (2004; before the trawl ban), June 2013 to May 2014 (2013–2014; immediately after the trawl ban), and June 2015 to May 2016 (2015–2016; 3.5 years after the trawl ban). HH: Harpiosquilla harpax, MN: Miyakella nepa, OI: Oratosquillina interrupta, OO: Oratosquilla oratoria. Significant differences are indicated by asterisks: *p < 0.05; **p < 0.01, ***p < 0.001.
Figure 4
Figure 4
Yearly comparison (2004, 2013–2014 vs. 2015–2016) of percentage abundance (ad) and biomass (eh) of three size classes for four stomatopod species in the western waters of Hong Kong, respectively. HH: Harpiosquilla harpax, MN: Miyakella nepa, OI: Oratosquillina interrupta, OO: Oratosquilla oratoria.
Figure 5
Figure 5
(a) The curvature of abundance (mean + SE) and (b) biomass (mean + SE) size spectrum at western waters from January 2004 to December 2004 (before the trawl ban) and June 2013 to May 2014 (2013–2014; immediately after the trawl ban), June 2015 to May 2016 (2015–2016; 3.5 years after the trawl ban). HH: Harpiosquilla harpax, MN: Miyakella nepa, OI: Oratosquillina interrupta, OO: Oratosquilla oratoria. Significant differences are indicated by asterisks: *p < 0.05; **p < 0.01.
Figure 6
Figure 6
Sampling locations of benthic crustaceans in the western waters of Hong Kong. W1.a, W1.b, W2, W3 and W4 indicate the location of the transects in the present study. The same transacts were surveyed throughout the entire study period, except W1.a which was surveyed only in 2004 (2004; before the trawl ban) and W1.b which was surveyed in June 2013 to May 2014 (2013–2014; immediately after the trawl ban) and June 2015 to May 2016 (2015–2016; 3.5 years after the trawl ban).

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