Natural mortality of three commercial penaeid shrimps (<em>Litopenaeus vannamei, L. stylirostris</em> and <em>Farfantepenaeus californiensis</em>) of the Gulf of California using gnomonic time divisions

Abstract

Summary:The estimation of natural mortality (M) is critical for stock assessment and fisheries management. The shrimp fishery is the most valuable one in Mexico and along the Pacific Coast of Mexico, and exploitation primarily targets three species: white (Litopenaeus vannamei), blue (L. stylirostris), and brown (Farfantepenaeus californiensis). It is a sequential fishery, so an appropriate estimate of M for different life stages is required for management purposes. Typically, M is estimated from the exploited stock, which is usually composed of adults, assuming a constant value for M, and this estimate is used for studies of population dynamics, stock assessments and determinations of the status of a fishery. In this study, we estimate M-at-age (i.e. life stage) for each species using the gnomonic time division model. The gnomonic intervals correspond to the actual life stages reported in the literature, whose duration was used for model fitting. The gnomonic model showed that M declines sharply in early life stages but declines to an asymptotic value after reaching maturity, and the model provided biologically consistent estimates of M at each life stage for the three shrimp species. Such estimates may be used with confidence to model the dynamics of sequential shrimp fisheries.Keywords: Gulf of California; natural mortality; sequential fishery; penaeid shrimps; gnomonic intervals. Mortalidad natural de tres camarones peneidos comerciales (Lithopenaeus vannamei, L. stylirostris y Farfantepenaeus californiensis) del Golfo de California usando intervalos de tiempo gnomónicosResumen: La estimación de mortalidad natural (M) es crítica para la evaluación de stocks y el manejo de las pesquerías. La pesquería de camarón es la de mayor valor en México y a lo largo de la costa del Pacífico de México, y la explotación tiene primariamente a tres especies como objetivo: blanco (Litopenaeus vannamei), azul (L. stylirostris) y café (Farfantepenaeus californiensis). Se trata de una pesquería secuencial, de tal suerte que para su manejo se requiere de una apropiada estimación de M para los diferentes estadios de vida. Típicamente M es estimada de stocks explotados, los cuales están usualmente compuestos de organismos adultos, se supone un valor de M constante y esta estimación es usada para estudios de dinámica de poblaciones, evaluación de stocks y determinación del estado de las pesquerías. En este estudio estimamos M-a-edad (p.ej. estadios de vida) para cada especie usando el modelo de intervalos de tiempo gnomónicos. La duración de los intervalos gnomónicos corresponde a los estadios de vida reportados en literatura, cuya duración fue usada para ajustar el modelo. El modelo de intervalos gnomónicos mostró que M declina rápidamente en estadios tempranos de vida, cambiando hacia un valor asintótico después de alcanzar la madurez. El modelo provée estimaciones de M biológicamente consistentes para cada estadio de vida para las tres especies. Estas estimaciones pueden ser usadas con confianza para modelar la dinámica de pesqu...

Reproductive and recruitment seasons for Penaeus aztecus in the Tamaulipas-Veracruz area, Gulf of Mexico

“…In the Gulf of Tehuantepec, monthly M rates were reported for the populations of P. californiensis (at 0.22), and P. vannamei (at 0.20) (Ramos-Cruz et al, 2006). Similar results were documented for the populations of P. californiensis, P. vannamei, and Penaeus stylirostris in the Gulf of California, Mexico (Aranceta-Garza et al, 2016).…”

Improving the gnomonic approach with thegnomonicMR-package to estimate natural mortality throughout different life stages

“…For the application of the improved gnomonic approach and to show the functionality of the gnomonicM package, gnomonicM was tested via the deterministic method and by comparing the estimates with the results of two species reported by Caddy (1996); the species had (i) seven gnomonic intervals, (ii) longevity of one year (365 days), (iii) egg stage durations of 2 days, and (iv) MLF values of 200,000 and 135 eggs. Additionally, the methodology was applied to published data that used the gnomonic model, and the estimates were compared with the results provided by the cited authors (see Ramírez-Rodríguez & Arreguín-Sánchez, 2003;Martínez-Aguilar, Arreguín-Sánchez & Morales-Bojórquez, 2005;Giménez-Hurtado, Arreguín-Sánchez & Lluch-Cota, 2009;Martínez-Aguilar et al, 2010;Aranceta-Garza et al, 2016;Romero-Gallardo et al, 2018 for details). This approach allowed the assessment of the application of gnomonicM for different taxa (fish and invertebrates) and life histories (demersal, pelagic, benthic, and short and long-life spans).…”

“…Later, the ''gnomonic model'' was modified and extended to long-lived species, including the addition of criteria for adjusting the number of gnomonic intervals to the duration of real-life stages, improving the biological sense of the approach, and incorporating variability in fecundity, thus providing estimates of uncertainty in the outputs (Martínez-Aguilar, Arreguín-Sánchez & Morales-Bojórquez, 2005). These changes increased the versatility and utility of the ''gnomonic model'' for estimating M in any marine and freshwater spawning species (Giménez-Hurtado, Arreguín-Sánchez & Lluch-Cota, 2009;Martínez-Aguilar et al, 2010;González-Peláez et al, 2015;Aranceta-Garza et al, 2016;Romero-Gallardo et al, 2018).…”

Peer Review #1 of "Evidence of overfishing of geoduck clam Panopea globosa from a length-based stock assessment approach (v0.1)"

“…A gnomonic interval is a systematic strategy for the unequal subdivision of the lifespan of an individual into time intervals, which increase in duration and proportion for each time interval. Therefore, in terms of elapsed time, two gnomonic intervals in a subdivided life history can be considered equivalent if they each form the same constant proportion of the time elapsed (Caddy, 1996;Ramírez-Rodríguez & Arreguín-Sánchez, 2003;Martínez-Aguilar, Arreguín-Sánchez & Morales-Bojórquez, 2005;Aranceta-Garza et al, 2016;Romero-Gallardo et al, 2018). Thus, the natural mortality of P. globosa was modeled as follows: 1) egg to trochophore larvae (24 hours); 2) early larvae (6.5 days); 3) late larvae (11 days); 4) early juveniles (35 days); 5) juveniles (3-9 months); 6) late juveniles (1-2 years); and 7) preadult to adults (3-47 years).…”