DOI: 10.5061/dryad.gf1vhhn02
title: Isotopic niche overlap of four large pelagic predatory fish species in the northwest Atlantic ocean

description: Understanding trophic dynamics and the potential for competition among
 pelagic predators is critical to managing multi-species fisheries. We
 estimated trophic position and isotopic niche overlap for albacore
 (Thunnus alalunga; n = 63), Atlantic bluefin tuna (Thunnus thynnus; n =
 16), bigeye tuna (Thunnus obesus; n = 70) and swordfish (Xiphias gladius;
 n = 20) collected from the northwest Atlantic in 2022 using stable isotope
 ratios of carbon (δ13C) and nitrogen (δ15N) in muscle. Atlantic bluefin
 tuna showed low overlap with other species, while bigeye tuna had high
 overlap with albacore and swordfish (particularly swordfish ≤ 175 cm in
 length). Large swordfish may avoid competition with other predators by
 foraging on deeper prey based on higher δ13C values. Different size
 incorporation methods differentially affected overlap estimates,
 necessitating careful consideration of methodology. Trophic position
 estimates were similar to results from 14 - 21 years ago (except for
 bigeye tuna), despite ecological changes in the region. Understanding
 trophic dynamics among pelagic predators is essential to managing a system
 expected to undergo further shifts caused by climate change.
description: The dataset is based off of stable isotope ratios of carbon and
 nitrogen from muscle samples collected four species of large pelagic fish
 species. The data were processed as shown in
 Supplemental Material 2 of the submitted manuscript and the .rmd file
 uploaded (Software in Related Works section). 
description: # Isotopic niche overlap of four large pelagic predatory fish species in
 the northwest Atlantic ocean
 [https://doi.org/10.5061/dryad.gf1vhhn02](https://doi.org/10.5061/dryad.gf1vhhn02) ## Description of the data and file structure The sampling for this study took place opportunistically at two commercial fishing wharves in south-west Nova Scotia between August 14 – 27, 2022. Sampled fish had either been commercially caught by rod and reel and landed at Wedgeport, NS (Atlantic bluefin tuna and albacore) or by a single long-line vessel landed at Woods Harbour, NS (albacore, bigeye tuna, and Atlantic swordfish). Dressed weight was recorded at the point of landing, and muscle tissue samples were collected as well. Muscle samples were dried and homogenized, and carbon and nitrogen isotopic composition was determined using a Delta V Advantage Mass Spectrometer.  ### Files and variables #### File: LP_Niche_CJFAS_Location_Data.csv **Description:** Approximate capture location for four pelagic fish species in the northwest Atlantic Ocean. ##### Variables * Site: Name of the area. * Latitude: Approximate latitude of capture in decimal degrees. * Longitude: Approximate longitude of capture in decimal degrees. * Species: Abbreviations of which species the location data corresponds to. BET - bigeye tuna, SWO - Atlantic swordfish, ALB - albacore, and BFT - Atlantic bluefin tuna.  #### File: LP_Niche_CJFAS_SIA_Data.csv **Description:** Main dataset providing the basis for the analysis. ##### Variables * Species: Latin name. * Common_Name: Common name for each sample.  * SampID: Sample ID number.  * Year_Sampled: The year that the sample was collected.  * Month_Sampled: The month that the sample was collected.  * Day_Sampled: The day of the month that the sample was collected. * PortSampled: The location (name of port) that the sample was collected - distinct from point of capture in LP_Niche_CJFAS_Location_Data.csv. * Dressed_Weight_kg: Dressed weight of the fish in kg. Dressed refers to having fins and the head removed at sea as part of commercial fishing practices. * RWT_kg: For Atlantic bluefin tuna, round weight (in kg) was available. * CFLcm: Curved fork length (in cm), only provided for Atlantic bluefin tuna. * SFLcm: Straight fork length (in cm), only provided for Atlantic bluefin tuna.  * Approximate_Capture_Location: Corresponds to approximate capture location, see LP_Niche_CJFAS_Location_Data.csv. for latitude/longitude information. * Comments: Any comments about the sample or data processing. * Identifier 1: University of Windsor isotope lab identification number for each sample.  * D13C: Stable isotope ratio of carbon in per mill of the sample. * percC: Percent carbon of the sample. * D15N: Stable isotope ratio of nitrogen in per mill of the sample. * percN: Percent nitrogen of the sample. * C_N: Carbon to nitrogen ratio of the sample. * Run: Name of the stable isotope sampling run.  #### File: bathy_data.RData **Description:** R datafile used to produce Figure 1 - the Study Area map. Generated by the .Rmd script in Software ## Code/software The data were analyzed in using R (Version 4.3.0), specifically the R Markdown file "LP_Niche_CJFAS_Analysis_v2.Rmd" (uploaded as Software in Related Works).  The required libraries are listed at the top of the .rmd file. Please ensure that the libraries are installed before running the code.  The code follows the structure of the manuscript, and produces each of the figures attached to the submitted manuscript.