Age, growth and mortality of Lutjanus alexandrei in estuarine and coastal waters of the tropical south-western Atlantic

Abstract

Summary Otolith‐based methods were used to determine life history traits of the endemic Brazilian snapper (Lutjanus alexandrei) in estuarine and coastal environments in the south‐western Atlantic. Fishes were caught as juveniles inside mangrove‐bordered estuaries by traditional corral fisheries whereas adults were captured at sea using motorboats with trap and gill nets. Fish were sampled during landings and 331 otolith pairs were extracted from L. alexandrei. Inshore mangroves comprised individuals of 0–4 years (mean: 2 years), while individuals in deeper reef environments were older (range: 3–22; mean: 8 years), indicating an ontogenetic shift at approximately age 3 or 4. Edge analysis was used to validate the annual deposition in the otoliths, suggesting that opaque growth rings were formed between April and September. Age‐at‐length data were used to predict L. alexandrei growth rates using the von Bertalanffy growth model from where the parameters were calculated: L∞ = 31 cm, k = 0.24, t0 = −1.26, r2 = 0.97. Mortality rates were estimated for coastal habitats, with Z = 0.22 and S = 0.78 year−1, based on ages 7–17. Additionally, evidence of ontogenetic migration is provided by age and size structure.

Spatial and temporal variability in the otolith chemistry of the Brazilian snapper Lutjanus alexandrei from estuarine and coastal environments

“…Further work is necessary to assess the importance of these factors on otolith accumulation. Despite confounding factors, these results seem to confirm that L. alexandrei occupy estuaries during their first year of life, moving to areas influenced by coastal processes as early as age 2 years as inferred from age studies (Aschenbrenner & Ferreira, ). Yet for general conclusions related to emigration patterns, larger sample sizes may be required.…”

“…The impacts that threaten the future of Brazilian mangroves include the diversion of freshwater flows, deterioration of water quality caused by pollutants and nutrients as well as conversion for development activities such as agriculture, aquaculture (mainly by shrimp farms), salt extraction and infrastructure, all of which contribute to the degradation and deforestation process (Santos et al, ). The present results indicate that ontogenetic shifts between estuarine and coastal habitats may occur for L. alexandrei and that these habitats are essential for recruitment to the adult population (Aschenbrenner & Ferreira, ). Connectivity integrity between juvenile and adult habitats is thus an essential consideration for fishery managers and should be included in management plans as well as other customary fishery management measures.…”

“…Examining habitat‐specific and age‐specific variation in element:Ca ratios allow inference of potential movement patterns of L. alexandrei between estuarine and coastal areas in Brazil. This life‐history model is supported by a positive relationship between size and age, and depths for Lutjanidae on the north‐eastern Brazilian coast (Frédou & Ferreira, ; Moura et al, ; Aschenbrenner & Ferreira, ).…”

“…Otoliths were then air dried and stored in plastic vials. A single otolith (right) were used for trace element analysis, as age had previously been determined in otolith (left) sections and used for age determination for stock assessment work [for details on age determination see Aschenbrenner & Ferreira ()]. Measurements for annuli distances were performed for ages 1–7 years ( n = 170) parallel to the sulcus acusticus from the nucleus to the proximal face using a stereomicroscope with reflected light on a black background (Fig.…”

“…One of the most common lutjanids on reefs in the south‐western Atlantic Ocean is the endemic, and recently described Brazilian snapper Lutjanus alexandrei Moura & Lindeman . Similar to congeners in the Caribbean Sea, this species resides in estuarine or nearshore nurseries before moving to coastal reef environments later in life (Aschenbrenner & Ferreira, ). Despite its ecological and economic importance, basic life history information for L. alexandrei is scarce (Fernandes et al, ; Aschenbrenner & Ferreira, ).…”