Temporal and spatial variations in the age and growth of larval blue marlin Makaira nigricans in Cuba

Abstract

Introduction Blue marlin, Makaira nigricans are the largest species in the Istiophoridae family. They are commercially important and are fished throughout the Gulf of Mexico and Caribbean Sea. Blue marlin fisheries are managed by the International Commission for the Conservation of Atlantic Tunas (ICCAT) along with NOAA’s NMFS Atlantic Highly Migratory Species. Blue marlin are listed as “vulnerable” on the IUCN red list due to population declines globally because of overfishing and management. Understanding the early life history dynamics of blue marlin are crucial for elucidating growth, spawning habitat, distribution, and survival. The larval stage is the most vulnerable (99% mortality) and is the base for life cycle. Larval studies have been conducted in the Gulf of Mexico, Straits of Florida, and the Bahamas (Serafy et al. 2003; Sponaugle et al. 2005), yet little is known regarding their early life history in and around Cuba which target blue marlin for fishing tournaments. Objectives: Develop an age and growth curve for larval blue marlin from Cuban waters. •Compare spatial variation in growth rates (north vs south stations). •Examine temporal variation between the 2015 and 2016 growth curves.

Methods Collection •Ichthyoplankton collected during oceanographic surveys in May 2015 and 2016. •MOCNESS from 0-100 m in 25 m depth bins, neuston nets 0-10m, 0-50 m. •Genetically identified using species-specific PCR amplification of the ND4 mitochondrial DNA gene region in collaboration with the VIMS lab. Lab Analysis •Subset of larvae from a size and spatial distribution were selected for aging. •Otoliths (2 sagitta and 2 lapilli) were extracted when possible (n= 157). •Increments were blindly counted twice along the longest axis (reading axis). •Length at age was tested using a 2-way analysis of covariance (ANCOVA).

Results •122 blue marlin from 38 stations (in 2015) and 55 blue marlin from 11 stations (in 2016) collected in Cuban waters (Figure 2). •Age growth curves were similar for both North (n=69) and South (42). •Temporal variation in growth was observed between 2015 (n=111) vs. 2016 (n=46).

Conclusion •There was no significant difference in growth between the North and the South in 2015, however, there was a slightly faster growth rate (F=0.589, p=0.445) in the North (0.1159) compared to the South (0.0956) (a). •Temporal variation in the age growth curves were significantly higher in 2015 with a growth rate of 0.1069 compared to 2016, 0.0839 (F=25.7, p= < 0.001 ) (b). •The growth rates of blue marlin in Cuba is comparable to Sponaugle et al. 2005 (0.1282). Future Research •Examine whether environmental conditions (SST) are reflected in the variable growth observed between year and region. •Compare growth rates between istiophorid species: sailfish, white and black marlins found in adjacent water masses.