Artisanal Green Turtle, <i>Chelonia mydas</i>, Fishery of Caribbean Nicaragua: I. Catch Rates and Trends, 1991–2011

<div><p>This is the first assessment of catch rates for the legal, artisanal green turtle, <i>Chelonia mydas</i>, fishery in Caribbean Nicaragua. Data were collected by community members, monitoring up to 14 landing sites from 1991 to 2011. We examined take levels, and temporal and spatial variability in catch rates for the overall fishery, by region, and community using General Additive Mixed Models (GAMMs). More than 171,556 green turtles were killed during the period, with a mean estimated minimum 8,169±2,182 annually. There was a statistically significant decline in catch rates overall. Catch rates peaked in 1997 and 2002, followed by a downward trend, particularly from mid-2008 to the end of the study period. Similar downward trends were evident in both study regions. Community specific catch rate trends also indicated declines with decreases ranging from 21% to 90%. Decrease in catch rates in Nicaragua is cause for concern even though the principal source rookery at Tortuguero, Costa Rica, shows an increase in nesting activity. Explanations for the apparent discrepancy between the increasing trend at Tortuguero and decreasing catch rate trends in Nicaragua include: i) an increase in reproductive output, ii) insufficient time has passed to observe the impact of the fishery on the rookery due to a time lag, iii) changes in other segments of the population have not been detected since only nesting activity is monitored, iv) the expansive northern Nicaragua foraging ground may provide a refuge for a sufficient portion of the Tortuguero rookery, and/or v) a larger than expected contribution of non-Tortuguero rookeries occurring in Nicaragua turtle fishing areas. Our results highlight the need for close monitoring of rookeries and in-water aggregations in the Caribbean. Where consumptive use still occurs, nations sharing this resource should implement scientifically based limits on exploitation to ensure sustainability and mitigate impacts to regional population diversity.</p></div

Trends in green turtle catch rates for Awastara (AW) landings in Puerto Cabezas (PC).

<p>Estimated conditional dependence of catch rates on time (A) with the y-axis selected to optimally display the results and (B) with the y-axis scale the same as for <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0094667#pone-0094667-g006" target="_blank">Fig. 6A</a> to facilitate comparison. Plot components are the same as in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0094667#pone-0094667-g004" target="_blank">Fig. 4A and 4B</a>. Also shown on the scale of the response is (C) trend in catch rates (average turtles/day) over time from 1996 to 2011, assuming average fishing effort for AW in terms of nets used and trip length for the period.</p

Recorded and estimated green turtle landings by region from the Caribbean coast of Nicaragua, 1991–2011.

<p>See <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0094667#s2" target="_blank">Methods</a> for a description of how estimates were calculated and <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0094667#pone.0094667.s006" target="_blank">Table S2</a> for recorded and estimated annual take by community.</p>a<p>Data source from 1994 to April 1997: Lagueux <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0094667#pone.0094667-Lagueux1" target="_blank">[18]</a>.</p><p>bRegión Autónoma Atlántico Norte (North Atlantic Autonomous Region).</p>c<p>Data source: Cecil Clark, Puerto Cabezas, Nicaragua.</p>d<p>Data source for 1992 and 1993: Sea Turtle Conservancy, Gainesville, FL (formerly Caribbean Conservation Corporation).</p>e<p>Región Autónoma Atlántico Sur (South Atlantic Autonomous Region).</p>f<p>Data source: Centro de Investigaciones y Documentación de la Costa Atlántica (CIDCA), Bluefields, Nicaragua.</p>g<p>Grand Total  =  sum of 1991–2011.</p

Recorded and estimated annual green turtle take by region for the Caribbean coast of Nicaragua.

<p>Numbers above bars are number of landing sites monitored each year. RAAN  =  Región Autónoma Atlántico Norte, RAAS  =  Región Autónoma Atlántico Sur. See <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0094667#pone.0094667.s005" target="_blank">Table S1</a> for information on which sites were monitored each year and <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0094667#pone.0094667.s006" target="_blank">Table S2</a> for minimum recorded and estimated annual take by community.</p

Green turtles, <i>Chelonia mydas</i>, being transported to slaughter in Bluefields, RAAS, Nicaragua.

<p>Photo credit C.J. Lagueux.</p

Community specific trends in green turtle catch rates for the Caribbean coast of Nicaragua.

<p>Estimated conditional dependence of catch rates on time by communities in the RAAN (A) AW (Awastara), (C) DK (Dakura), and (E) SB (Sandy Bay), and in the RAAS (B) BS (Sandy Bay Sirpi), (D) RG (Río Grande Bar), (F) SN (Set Net Point) and (G) TA (Tasbapauni). Seasonality is also included in the community level model, and although the seasonal pattern in catch rates is the same as for the overall and regional models, the variance explained by seasonality is much less than before (as shown in Fig. 6H) when considering catch rates at the community level. Plot components are the same as in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0094667#pone-0094667-g004" target="_blank">Fig. 4A and 4B</a>. Note that the same y-axis scale is used for each variable (with the exception of month). The x-axis scale corresponds to the time periods when sampling took place (December 1995 to 2011 in all communities, except BS and RG in the RAAS where sampling started in 1991).</p

Survival rate estimates for wild populations of green turtles.

a<p>Unless otherwise stated, all size data is straight carapace length measured from the midpoint of the nuchal notch to the most posterior tip of the longest posterior marginal scute. CCL  =  curved carapace length measured from the midpoint of the nuchal notch along the curve of the midline to the posterior end of the carapace.</p>b<p>S = true survival; Φ = apparent survival.</p>c<p>Patrício et al. <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0094667#pone.0094667-Patrcio1" target="_blank">[85]</a> acknowledged estimate is likely low due to permanent emigration, and human induced mortality was considered unlikely but cannot be ruled out entirely.</p>d<p>Seminoff et al. <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0094667#pone.0094667-Seminoff2" target="_blank">[96]</a> cautioned about reliability of survival probability estimate due to small sample size.</p

Caribbean coast of Nicaragua.

<p>Approximate green turtle, <i>Chelonia mydas</i>, foraging and fishing areas, principal green turtle fishing communities, and commercial centers; including the Tortuguero, Costa Rica, rookery. Modified from Lagueux et al. <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0094667#pone.0094667-Lagueux5" target="_blank">[46]</a>. Baseline map created using SEATURTLE.ORG Maptool <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0094667#pone.0094667-SEATURTLEORG1" target="_blank">[109]</a>.</p

Generalized Additive Mixed Model (GAMM) analysis results for green turtle catch data from the Caribbean coast of Nicaragua.

<p>For each model its AIC value and the difference in AIC values between the top ranked model (value in bold) and other models (<b>Δ</b>AIC) is shown. Models are sorted by analysis type: overall, regional (when applicable), and community level (with the “best” model in terms of smallest AIC value in <b><i>bold italics</i></b> by analysis level and in <b><u>bold underline</u></b> overall).</p><p>Results are shown for the three data sets analyzed: COM  =  principal fishing community data, AW COMCTR  =  commercial center data for the Awastara community, PCFA  =  Pearl Cays fishing area data. Explanatory variable acronyms are: TM  =  TIME, MN  =  MONTH, RG  =  REGION, CM  =  single or aggregated community, TIME by  =  interaction between TIME and either REGION or community.</p><p>For terms included in a model, p-values were indicated as follows: *** = <0.001 or ** = <0.01 and values >0.1 are designated as non-significant (NS), with results for the three data sets considered separated by a semi-colon.</p>a<p>“X” indicates when temporal autocorrelation was treated using an autoregressive model of order one.</p

Overall trends in green turtle catch rates for communities fishing in Refugio de Vida Silvestre Cayos Perlas.

<p>Estimated conditional dependence of catch rates on (A) time and (B) month. Plot components are the same as in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0094667#pone-0094667-g004" target="_blank">Fig. 4A and 4B</a>. Also shown on the scale of the response is (C) trend in catch rates (average turtles/day) over time from 1996 to 2011, assuming average fishing effort across the four communities in terms of nets used and trip length. The four communities included in the analysis were: Haulover, Kahkabila, Pearl Lagoon, and Set Net Point.</p