Length‐Based Stock Assessment of the Mackerel Scad, Decapterus macarellus (Cuvier, 1833) From the Tanzanian Coastal Waters
Joseph Salawa Sululu
Blandina Robert Lugendo
Paul Tuda
Benaiah Lameck Benno
Abstract
This study aimed to conduct a stock assessment of Decapterus macarellus from Tanzanian coastal waters to determine its current stock status and provide appropriate management recommendations. We used a suite of length-based methods, including the Electronic Length Frequency Analysis (ELEFAN) programme to estimate growth parameters and catch curves to evaluate exploitation fishing and mortality parameters; Length-Based Spawning Potential Ratio (LBSPR) to calculate the spawning potential ratio (SPR), length-based indicators (LBI) to assess sustainable fishing levels and length-based reference point (LBRP) to determine the target reference point (RP) for stock spawning biomass (SB). The results indicated that this small pelagic species grows fast, with a growth rate (K) of 0.74 year−1 and a growth performance index (Ф′) of 2.88. However, the stock is currently at risk of overfishing due to high fishing pressure (F/M > 1) and an elevated exploitation rate (E = 0.71), which resulted in a very low SPR (SPR = 0.11) and SB below the target RP. Yield-per-recruit analysis revealed that the current fishing effort (Fcurr = 2.57) far exceeded the precautionary limit (F0.1) and surpassed the fishing mortality rate that maximizes yield per recruit (Fmax = 1.73). This excessive effort largely impacted mega-spawners, reducing their proportion in the catch to a critically low percentage (9%). On the basis of these findings, the study recommends reducing the current fishing effort to F0.1 (0.84) by limiting the number of ring nets, implementing seasonal closures during peak spawning periods and operating in deeper waters (40–200 m) to protect juveniles and minimize mega-spawner capture.
Sululu J.S., Lugendo B.R., Tuda P. and Benno B.L. (2025) Length‐Based Stock Assessment of the Mackerel Scad, Decapterus macarellus (Cuvier, 1833) From the Tanzanian Coastal Waters. Aquaculture Fish and Fisheries 5(1). 10.1002/aff2.70039
@article{Sululu2025,
Title = {Length‐Based Stock Assessment of the Mackerel Scad, Decapterus macarellus (Cuvier, 1833) From the Tanzanian Coastal Waters},
Author = {Sululu, Joseph Salawa and Lugendo, Blandina Robert and Tuda, Paul and Benno, Benaiah Lameck},
Editor = {},
Journal = {Aquaculture Fish and Fisheries},
Year = {2025},
Volume = {5},
Doi = {10.1002/aff2.70039},
Abstract = {This study aimed to conduct a stock assessment of Decapterus macarellus from Tanzanian coastal waters to determine its current stock status and provide appropriate management recommendations. We used a suite of length-based methods, including the Electronic Length Frequency Analysis (ELEFAN) programme to estimate growth parameters and catch curves to evaluate exploitation fishing and mortality parameters; Length-Based Spawning Potential Ratio (LBSPR) to calculate the spawning potential ratio (SPR), length-based indicators (LBI) to assess sustainable fishing levels and length-based reference point (LBRP) to determine the target reference point (RP) for stock spawning biomass (SB). The results indicated that this small pelagic species grows fast, with a growth rate (K) of 0.74 year−1 and a growth performance index (Ф′) of 2.88. However, the stock is currently at risk of overfishing due to high fishing pressure (F/M > 1) and an elevated exploitation rate (E = 0.71), which resulted in a very low SPR (SPR = 0.11) and SB below the target RP. Yield-per-recruit analysis revealed that the current fishing effort (Fcurr = 2.57) far exceeded the precautionary limit (F0.1) and surpassed the fishing mortality rate that maximizes yield per recruit (Fmax = 1.73). This excessive effort largely impacted mega-spawners, reducing their proportion in the catch to a critically low percentage (9%). On the basis of these findings, the study recommends reducing the current fishing effort to F0.1 (0.84) by limiting the number of ring nets, implementing seasonal closures during peak spawning periods and operating in deeper waters (40–200 m) to protect juveniles and minimize mega-spawner capture.},
}
TY - JOUR
AU - Sululu, Joseph Salawa
AU - Lugendo, Blandina Robert
AU - Tuda, Paul
AU - Benno, Benaiah Lameck
TI - Length‐Based Stock Assessment of the Mackerel Scad, Decapterus macarellus (Cuvier, 1833) From the Tanzanian Coastal Waters
T2 - Aquaculture Fish and Fisheries
PY - 2025
VL - 5
DO - 10.1002/aff2.70039
AB - This study aimed to conduct a stock assessment of Decapterus macarellus from Tanzanian coastal waters to determine its current stock status and provide appropriate management recommendations. We used a suite of length-based methods, including the Electronic Length Frequency Analysis (ELEFAN) programme to estimate growth parameters and catch curves to evaluate exploitation fishing and mortality parameters; Length-Based Spawning Potential Ratio (LBSPR) to calculate the spawning potential ratio (SPR), length-based indicators (LBI) to assess sustainable fishing levels and length-based reference point (LBRP) to determine the target reference point (RP) for stock spawning biomass (SB). The results indicated that this small pelagic species grows fast, with a growth rate (K) of 0.74 year−1 and a growth performance index (Ф′) of 2.88. However, the stock is currently at risk of overfishing due to high fishing pressure (F/M > 1) and an elevated exploitation rate (E = 0.71), which resulted in a very low SPR (SPR = 0.11) and SB below the target RP. Yield-per-recruit analysis revealed that the current fishing effort (Fcurr = 2.57) far exceeded the precautionary limit (F0.1) and surpassed the fishing mortality rate that maximizes yield per recruit (Fmax = 1.73). This excessive effort largely impacted mega-spawners, reducing their proportion in the catch to a critically low percentage (9%). On the basis of these findings, the study recommends reducing the current fishing effort to F0.1 (0.84) by limiting the number of ring nets, implementing seasonal closures during peak spawning periods and operating in deeper waters (40–200 m) to protect juveniles and minimize mega-spawner capture.
ER -
