Development of Low-Resistance Coastal Stow Net Using Numerical Analysis and Model Experiments

Abstract

In coastal stow net fishing, the heavy weight of a typical anchor (750–1000 kg) can increase the risk of capsizing the boat and crew member injury during hoisting operations. Thus, to prevent these accidents, a reduction in the anchor weight is required. One strategy to achieve this is to reduce the resistance force of the fishing gear used, which would allow lighter anchors to be employed. This requires the accurate estimation of the resistance force for various gear designs. Therefore, the resistance force and shape during the operation of two representative types of coastal stow nets currently employed in the Korean coastal stow net fishing industry were investigated using simulations and modeling experiments. The modeled fishing gear was divided into four sections according to the mesh size. Based on the results, the twine thickness was reduced in order to target areas of the gear where the greatest resistance was observed, while the front part of the gear was redesigned to prevent the front of the net from being pushed back into a suboptimal shape. The proposed low-resistance fishing gear has the potential to improve occupational safety in the coastal stow net fishing industry.

1. Introduction

Coastal stow net fishing in Korea typically involves the use of non-powered or powered vessels weighing less than 8 tons, with two to five crew members using three to five units of fishing gear with a mesh size of 25 mm or more. A single anchor is generally used to secure the fishing gear in strong tidal currents, particularly the western coast of Korea, with the help of the tide pushing fish into the net [1,2] (Figure 1). The primary target species for coastal stow net fishing include anchovy, short-arm octopus, swimming crab, hairtail, and other fish species.

Coastal stow nets are deployed in waters with a high flow velocity, which the fishing vessel has to navigate against. In addition, in deep fishing grounds, stow nets, which are characterized by high flow resistance, and the anchors required to hold them in place are repeatedly cast out and hauled in. During this process, accidents may occur due to the combined weight of the anchor (750–1000 kg) and fishing gear, risking injury to crew members and damage to the fishing vessel and equipment. In particular, capsizing events and negligence in Korean coastal stow net fisheries are responsible for an average of 56 and 146 accidents each year, respectively. The risk of capsizing is higher for stow net fishing boats because of their lighter hull and high deck loads, which leads to a higher center of gravity. During hoisting operations, if the anchor becomes stuck, the strong tension on the rope can apply excessive force to the hull. In addition, poor attention to safety during the lifting of stow nets would lead to physical injury, such as body parts being caught in side rollers.

Previous studies conducted on coastal stow nets have focused on methods for improved stow nets and dissemination [3], the estimation of the maximum sustainable yield (MSY) and the community structure of the fish captured [4], the optimization of current stow net fishing methods and fishing yields [5,6,7], and numerical modeling of net performance [8,9,10,11,12,13]. However, to the best of our knowledge, no previous studies have focused on the optimization of coastal stow net fishing gear to reduce the risk of accidents during operation.

Because Korean coastal stow nets use heavy anchors to anchor the gear in strong currents, this study investigated a method to reduce the resistance of the fishing gear, which would then allow the anchor weight to be reduced. This would serve to prevent accidents that may occur during the hoisting of the anchor and fishing gear. Through model experiments and a numerical analysis of two representative designs for coastal stow nets, we determined the resistance force and proposed design improvements to reduce the resistance force of fishing gear.

2. Materials and Methods

2.1. Coastal Stow Nets

This study examined two types of coastal stow nets (referred to as Types A and B) currently in use in Chungcheongnam-do, Republic of Korea (Figure 2a,b, and Tables S1 and S2). The typical fishing depth for coastal stow nets is 25 m, with an average tidal current speed of 0.7 m/s, utilizing an anchor weighing 750–1000 kg. Type A, which was a knotted net, had a length of 124.51 m, while Type B, which included a Raschel net, had a length of 127.95 m. The kites for both types of nets measured 2 m in width and 12 m in height, with three pieces connected vertically and positioned on the left, right, and side of the fishing gear (Figure 2c).

2.2. Mathematical Model

A mass-spring model was employed to mathematically describe the coastal stow net fishing gear. This model is commonly utilized in research analyzing underwater complex flexible structures [11,12,13]. It divides a fishing gear system into a finite number of small elements, assigning a mass to the connection point of each element, and introducing a spring between the two mass points, thus creating a structure connected by springs. In this study, the kite, mesh knot, float, sink, and other components of the coastal stow net fishing gear were considered mass points, while the mesh bar was assumed to function as a spring.

2.2.1. Equation of Motion

The basic equation of motion for each mass was described as shown in Equation (1):

$$\left(M+∆M\right)\ddot{q}=F_{int}+F_{ext}$$

(1)

where $M$ is the total mass of a point, $∆M$ is the added mass, $\ddot{q}$is the acceleration vector, $F_{int}$is the internal force between the mass points, and $F_{ext}$ is the external force acting on the mass points.

The added mass was described as follows:

$$∆M={\rho }_w{V}_n{K}_m$$

(2)

where ${\rho }_w$is the density of seawater, $V_n$ is the volume of the mass point, and $K_m$ is the added mass coefficient, which was set at 1.5 because the structural connections were assumed to be spheres [14,15].

Cylindrical structures, such as ropes, were described using Equation (3) [16]:

$$K_m=1+\sin \mathsf{\alpha }$$

(3)

where $\alpha$ is the angle of attack.

2.2.2. Internal and External Forces

Internal Forces

Internal force was generated through the tension and compression of the springs connecting each mass point. This force acted on the net bar, linking the knots of the net, and on the ropes connecting various parts of the fishing gear. Both the rope and twine were treated as massless springs, allowing the internal force equation to be expressed as follows:

$$F_{int}=-{\sum }_{i=1}^n{k}_i{n}_i\left(\left|r_i\right|-l_i^0\right)$$

(4)

where $k$ is the stiffness of the spring, $n$ is the unit vector of the spring direction, $r$ is the position vector of the spring, and $l^0$is the initial length of the spring.

The stiffness of the spring was calculated as follows:

$$k={\displaystyle \frac{EA}{l^0}}$$

(5)

where $E$ is Young’s modulus of the material, and $A$is the effective cross-sectional area of the material [16].

External Forces

The external forces consisted of the drag force ($F_D$), lift force ($F_L$), and buoyancy or sinking force ($F_B$), with these external forces acting on the fishing gear system only through the mass point (Figure 3).

The external force can be expressed as follows [10]:

$$F_{ext}=F_D+F_L+F_B$$

(6)

where $F_D$is the resistance force, $F_L$is the lift force, and $F_B$ is the buoyancy and sinking force.

The drag and lift forces were calculated as follows:

$$F_D=-{\displaystyle \frac{1}{2}}{C}_D{\rho }_{w}S{V}^2{n}_v$$

(7)

$$F_L={\displaystyle \frac{1}{2}}{C}_L{\rho }_{w}S{V}^2{n}_L$$

(8)

where $C_D$ is the drag force coefficient, $S$ is the projected area of the mass point, qw is the density of seawater, $V$ is the magnitude of the resultant velocity vector, $n_v$ is the unit vector of the resultant velocity vector, $C_L$ is the lift force coefficient, and $n_L$ is the direction of the lift force at a right angle to the drag.

The drag and lift coefficients for a plane net in accordance with the attack angle are presented in Figure 4 [16].

$n_L$ was calculated as

$$n_L={\displaystyle \frac{(V\times r)\times V}{\left|(V\times r)\times V\right|}}$$

(9)

where $V$ is the resultant velocity vector.

$V$ is composed of the motion velocity vector of the mass point $V_m$ and the current velocity vector $V_c$:

$$V=V_m-V_c$$

(10)

The attack angle formed by the bar and the resultant velocity vector were obtained from

$$\alpha ={\cos }^{-1}\left[{\displaystyle \frac{V·r}{\left|V\right|·\left|r\right|}}\right]$$

(11)

The buoyancy and sinking force ($F_B$) were described as follows:

$$F_B=({\rho }_i-{\rho }_w)V_{N}g$$

(12)

where ${\rho }_i$ is the density of the material, $V_N$is the volume of the mass, and $g$ is the acceleration of gravity.

2.3. Solution Method

Considering both the external and internal forces, the equation of motion was converted into the following non-linear second-order differential equation in the time domain.

$$M\ddot{q}\left(t\right)=F_{int}\left(t\right)+F_D\left(t\right)+F_L\left(t\right)+F_B\left(t\right)$$

(13)

where $M$ is the total mass of the point and $\ddot{q}$ is the acceleration.

Equation (13) was converted into Equation (15) as follows:

$$\dot{q}\left(t\right)=V_m\left(t\right)$$

(14)

$${\dot{V}}_m\left(t\right)=M^{-1}\left[F_{int}\left(t\right)+F_D\left(t\right)+F_L\left(t\right)+F_B\left(t\right)\right]$$

(15)

In this study, the resistance force of the two types of coastal stow nets was calculated using the fourth-order Runge–Kutta method.

2.4. Simulation Conditions

The two types of coastal stow net fishing gear were numerically modeled in three-dimensional space, and the simulations of stow nets were conducted. Then, the resistance force of each section, which is divided by the mesh size, was analyzed. These sections were determined according to the mesh size (Figure 5). The flow velocity conditions vary depending on where coastal stow net fishing is conducted (generally 0.7–1.2 m/s in Korea); the present study considered five flow velocities, ranging from 0.3 to 1.1 m/s at 0.2 m/s intervals. This range included flow velocities that were lower than expected for real fishing conditions in order to assess the spreading process for the gear. The depth of the fishing gear was set at 50 m, and calculations were conducted at 0.0001 s intervals.

Numerical simulations were conducted under these conditions to compare the variation in the net shape of the Type A and Type B coastal stow nets and the resistance force of the individual sections according to changes in flow velocity for identifying the sections of the fishing gear where the greatest resistance force occurs. To increase the calculation efficiency of the simulation, the mesh grouping method was employed [12].

2.5. Model Experiment

For the model experiments, a flume tank installed at the National Institute of Fisheries Science, Busan, Korea, was used. The overall dimensions of the tank were 25.12 m (W) × 4.50 m (L) × 8.27 m (H), with the observation section measuring 8.0 m (L) × 2.8 m (W) × 1.4 m (H) (Figure 6). Two experiments were conducted in July and August 2022. A 1/50 scale model of the fishing gear was installed in the center of the tank, and changes in the resistance force and shape were measured for five flow velocities ranging from 0.3 to 1.1 m/s at 0.2 m/s intervals. The measurements were taken at 0.0001 s intervals.

The resistance force was measured using a load cell (Summ (SP)-10K, Senstech, Busan, Republic of Korea), and the flow velocity was measured using a propeller-type current meter (VOT 2-200-20, Kenek, Tokyo, Japan). Measurements were monitored with data collection equipment and converted to full-scale values. The resistance force, obtained from the load cell, was received as an analog signal through an amplifier (DN-AM310, Dacell, Cheongju, Chungcheongbuk-do, Republic of Korea), a wave generator (BNC-2090A, National Instruments, Austin, TX, USA), and a data acquisition (DAQ) device (PCI-6034E, National Instruments, Austin, TX, USA). The data were saved to the computer on which the analysis software was installed. To capture variation in the shape of the model fishing gear, a digitizer and cameras were positioned at the front, to the side, and on the bottom of the tank. In the tank experiment using the model fishing gear, the height of the mooring point distanced from the bottom of the tank was 0.5 m. Interpolation was used to compare the experimental results with the simulation values.

(1)

Similarity law

The two types of model fishing gear used in the model experiment were produced using Tauti’s similarity law [17,18,19]. The hanging ratio of the fishing gear used in the experiment was 30% and 95.4% in terms of width and length, respectively, and the similarity ratio ($\mathsf{\Lambda }$) was reduced to 1/50 of the original size based on the size of the tank and the scaling effect.

$${\displaystyle \frac{{\lambda }_2}{{\lambda }_1}}=\mathsf{\Lambda }$$

(16)

$${\displaystyle \frac{d_1}{l_1}}={\displaystyle \frac{d_2}{l_2}}$$

(17)

$$V^2={\left({\displaystyle \frac{v_2}{v_1}}\right)}^2={\displaystyle \frac{d_2\left({\rho }_2-1\right)}{d_1\left({\rho }_1-1\right)}}$$

(18)

$${\displaystyle \frac{F_2}{F_1}}={\mathsf{\Lambda }}^2{V}^2$$

(19)

where ${\lambda }_1$and ${\lambda }_2$ are the dimensions of each component of the original and model gear, respectively; $l_1,d_1$and$l_2,d_2$ are the bar length and diameter of twine in the original and model nets, respectively; ${\rho }_1$ and ${\rho }_2$ are the densities of the material in the original and model nets, respectively; $F_1$and $F_2$ are the ratios of the buoyancy, sinking force, and fluid resistance acting on the original and model nets, respectively; $v_1$and $v_2$ are the flow velocities for the original and model nets, respectively; and V is the flow velocity ratio of the real and model nets.

2.6. Model Fishing Gear

The specifications for the scaled-down version of the two net types are presented in

Table 1. Specifications for the 1/50 scale models of the Type A and B coastal stow nets.

	Type A	Type B
Float
Material	Plastic	Plastic
Diameter (mm)	15	15
Total buoyancy (N)	0.014	0.014
Number of floats	14	14
Net
Material	PE/NYLON	PE/NYLON
Total length (m)	2.494	2.550
Diameter (mm)	0.7, 0.7, 0.5, 0.7, 0.6, 1.0	0.7, 0.7, 0.5, 0.7, 0.6, 0.7, 0.6, 1.2

. To quantify the resistance force generated by the fishing gear, we applied Tauti’s similarity law to create a 1/50 scale model of the Types A and B nets (

Table 2. Similarity ratios for the 1/50 scale models of the Types A and B coastal stow nets.

	Type A	Type B
$\mathsf{\Lambda }$	1/50	1/50
${\displaystyle \frac{d}{l}}$ (Section 1)	0.025	0.033
$V=\sqrt{{\displaystyle \frac{d_2}{d_1}}}$	1.95	1.78
${\displaystyle \frac{F_2}{F_1}}={\mathsf{\Lambda }}^2{V}^2$	0.0015	0.0013
$S_n$(Section 1)	0.051	0.066

and Figure 7).

2.7. Altering the Twine Thickness in Section 1 to Reduce Flow Resistance

To analyze the flow resistance and gear shape variation that occur in the two types of fishing gear as a result of reducing the twine thickness in Section 1 (see Figure 5), 1/2 (Case 1), 1/3 (Case 2), and 2/3 (Case 3) of the original twine thickness (Case 0) were tested (

Table 3. Modification of twine diameter for Section 1.

	Case 0 (Original)	Case 1 (1/2 Twine Thickness)	Case 2 (1/3 Twine Thickness)	Case 3 (2/3 Twine Thickness)
Section 1 (mm)	3.48	1.74	1.16	2.32
	3.20	1.60	1.07	2.12
	2.56	1.28	0.85	1.70
	2.26	1.13	0.75	1.50
	2.09	1.05	0.70	1.39
	2.09	1.05	0.70	1.39
	1.91	0.96	0.64	1.27
	1.91	0.96	0.64	1.27

).

3. Results and Discussion

3.1. Analysis of Resistance Force and Shape Variation via Simulation and Model Experiments

3.1.1. Resistance Force Analysis

The resistance force generated by fishing gear Types A and B was simulated at a depth of 50 m with a flow velocity range of 0.3 to 1.1 m/s at intervals of 0.2 m/s, while a 1/50 scale model was also tested in experiments. The resistance force increased as the flow velocity increased in both the simulation and model experiments. The simulation and experimental results revealed that the resistance force of the Type B net was 6.3% and 19.5% higher, respectively, than that of Type A at a flow velocity of 1.1 m/s. The resistance force of Type B was higher because Raschel netting was used in Section 3 (see Figure 5). The difference in the resistance observed between the simulations and the model experiments was assumed to be due to a combination of factors, including errors associated with the interpolation methodology used to convert the experimental results to a same flow velocity that used in the simulation, errors inherent in the scale-down model, and errors inherent in the simulation model (Figure 8). This study also did not consider the potential additional frictional resistance caused by factors such as seabed contact, which could be significant in real fishing ground scenarios.

3.1.2. Shape Variation Analysis

The shape variation in the fishing gear according to flow velocity was measured at 0.2 m/s intervals from 0.3 to 1.1 m/s. In the experiments and simulations, the width and height of the Type A net increased by 4% and decreased by 1.5%, respectively, while that for Type B increased by 3.2% and decreased by 11.7%, respectively, within the flow velocity range of 0.7 to 1.1 m/s, which is typically used for operation. In addition, compared to a flow velocity of 0.3 m/s, the net mouth area decreased by 30% and 36% for Type A and 19% and 26% for Type B, respectively, at flow velocities of 0.7 m/s and 1.1 m/s, respectively (

Table 4. Shape variation in the Type A and B nets for Case 0 with different flow velocities in the model experiments.

		Flow Velocity (m/s)
		0.3	0.5	0.7	0.9	1.1
Width (m)	Type A	19.65	19.80	20.10	20.55	20.90
	Type B	19.80	19.95	20.35	20.60	21.00
Height (m)	Type A	32.55	25.75	22.30	19.95	19.65
	Type B	27.65	25.50	21.80	19.75	19.25

). A comparison of the net mouth area of Type A and Type B by flow velocity shows that the most significant difference occurs at a flow velocity of 0.3 m/s. This difference is presumably attributable to the insufficient spreading of the net mouth at low velocities. To obtain a more accurate comparison, a flow velocity of 0.7 m/s or higher is more appropriate.

In the model experiments and simulations, net sagging was observed to occur in the areas indicated by the red circles in Figure 9 and Figure 10. This was caused by the side panels of the net being held by the bridle at the front part of the net, while the top and bottom panels of the net were pushed back. Improvements to the front part of the net are thus necessary to prevent the sagging of the net because this creates additional hydrodynamic resistance.

3.2. The Analysis of the Simulated Sectional Resistance Force for the Coastal Stow Nets

Because the model experiments could only analyze the total resistance force of the fishing gear, simulations were used to analyze the resistance force by section. For Case 0, the resistance force in Section 1 accounted for 48.7–70.6% of the total resistance force for all flow velocities in both the Type A and B nets (Figure 11 and Figure 12). These results indicate that a reduction in resistance may be possible by improving Section 1.

By varying the twine thickness in Section 1, the highest reduction in resistance was observed for Case 2. In all cases, the simulation results for Type A showed that, as the flow velocity increased, the proportion of resistance generated by Section 1 decreased, while the proportion of resistance generated by Sections 2 and 3 increased. This indicated that, at low flow velocities, the net in Section 1 is not fully spread and the flow does not readily penetrate the net, resulting in a high resistance force. However, as the flow velocity increased, the front part of the net in Section 1 spread as designed, resulting in a decrease in the proportion of resistance generated by the entire fishing gear. Sections 2 and 3 exhibited the opposite trend, with the smoother flow past Section 1 resulting in an increase in the resistance force in the other sections.

The simulation results for Type B differed from those for Type A because Raschel netting was used in Section 3. Therefore, the proportion of the overall resistance generated by Section 3 increased as the flow velocity increased. Furthermore, the mesh size in Section 4 was markedly smaller than that in Sections 1–3, which indicates that the proportion of resistance generated by the entire gear also increased as the flow velocity increased.

When reducing the twine thickness in Section 1 relative to the current gear (Case 0) at a flow velocity of 1.1 m/s, resistance reductions of 14% for Case 1, 19.4% for Case 2, and 6.8% for Case 3 were observed for the Type A net, while resistance reductions of 13.3%, 18%, and 8.5%, respectively, were observed for Type B.

3.3. Development of Low-Resistance-Force Fishing Gear

Low-Resistance-Force Fishing Gear

In the previous section, Case 2 was found to be the optimal scenario for the coastal stow nets, reducing the resistance across the entire gear by 19.4% and 18.0% for Types A and B, respectively. However, a net with the twine thickness used in Case 2 is not commercially available in the market, so the twine thickness used in Case 1 was employed for the development of low-resistance-force gear based on the supply of materials on site, while the material for the net was changed to ultra-high-molecular-weight polyethylene (UHMWPE). In order to prevent the negative hydrodynamic effects caused by the net being pushed back by the upper and lower panels of the front part of the gear (see Section 3.2), the front part of the gear was redesigned in a manner analogous to the wing part of a trawl gear, as illustrated in Figure 13. The redesign was based on the findings of the analysis conducted on the shape of the Type A and B nets.

Following the design stage, 1/50 scale models of the newly developed low-resistance-force fishing nets were constructed to compare their performance with that of the currently used Types A and B (Figure 14). The associated gear specifications are summarized in

Table 5. Specifications for the scale model of the low-resistance-force coastal stow net.

Item	Specification
Float
Material	Plastic
Diameter (mm)	15
Total buoyancy (N)	0.014
Number of floats	14
Net
Material	PE/NYLON
Total length (m)	2.494
Diameter (mm)	0.6, 0.5, 0.5, 0.7, 0.6, 1.0

.

3.4. Comparative Analysis of Types A and B and Low-Resistance-Force Coastal Stow Nets

Simulations and model experiments were conducted using the low-resistance-force fishing gear with the Case 1 twine diameter for Section 1. The low-resistance gear exhibited a significantly lower resistance than the Types A and B gear for all of the tested flow velocities in the simulation and experiments. In particular, the low-resistance gear had 26% and 28% lower resistance than the Type A gear and 30% and 39% lower resistance than the Type B gear at a flow velocity of 1.1 m/s in the simulation and experiments, respectively (

Table 6. Resistance force of Types A and B and the low-resistance-force coastal stow nets in simulations and model experiments.

			Flow Velocity (m/s)
			0.3	0.5	0.7	0.9	1.1
Resistance force (kgf)	Type A	Simulation	757	1878	3340	5498	7840
		Model	586	1518	2840	4535	6589
	Type B	Simulation	773	2000	3597	5864	8335
		Model	786	1945	3533	5517	7875
	Low resistance	Simulation	635	1465	2576	4059	5797
		Model	494	1291	2429	3896	4750

). The reason why the reduction in resistance was higher when compared to Type B was that Type B had Raschel netting in Section 3 (see Figure 5b), while the low-resistance gear did not, as was the case for Type A. The overall lower resistance was not only due to the use of smaller-diameter twine for Section 1 but also due to improvements in the design of the front part of the gear.

The shape analysis of the developed low-resistance gear revealed that the sagging observed in the Types A and B nets was effectively addressed by redesigning the front part of the gear. As a result, the mouth area of the net at a flow velocity of 1.1 m/s increased by 10% and 12% when compared to Types A and B, respectively, in the model experiments (

Table 7. Shape variation in the low-resistance fishing gear according to the flow velocity in simulations and model experiments.

		Flow Velocity (m/s)
		0.3	0.5	0.7	0.9	1.1
Simulation	Width (m)	13.2	14.5	15.1	15.8	18.8
	Height (m)	43.9	42.7	39.0	37.2	35.7
Model experiment	Width (m)	21.0	21.4	21.95	21.55	21.7
	Height (m)	31.6	26.5	22.75	20.9	20.9

and Figure 15), thus confirming the effectiveness of the proposed design changes.

4. Conclusions

To reduce the resistance force generated by fishing gear in coastal stow net fishing, our study examined the resistance force of the entire fishing gear structure and shape variation in the fishing gear in response to different flow velocities through simulation and model experiments.

(1)

This study revealed that resistance force in coastal stow net fishing gear, particularly in Section 1, increased with higher flow velocities. Section 1 accounted for a significant portion of the total resistance force, ranging from 48.7% to 61.4% for Type A and 57.5% to 70.6% for Type B. Based on these results, modifications were made to Section 1 to reduce resistance force by changing the twine thickness and the material to UHMWPE. Case 2, which had the smallest twine diameter, produced the most significant reduction in the resistance force.

(2)

The shape variation in the Types A and B fishing gear exhibited similar characteristics as the flow velocity increased, including a reduction in height and an increase in net width. Moreover, the upper and bottom panels of the gear were pushed backward by the front part of both types of the gear.

(3)

A resistance analysis of each section of the gear was conducted, with the findings from Case 1, which could be employed in the field, applied to Section 1. The front part of the gear was redesigned to resemble the wing net of a trawling gear, with the aim of preventing sagging. Simulation and model experiments were carried out to compare the resistance of the redesigned gear with that of Type A and B gears, with the results demonstrating that the resistance was reduced by 26% and 30% in simulations and 28% and 39.7% in the model experiments, respectively. In addition, the low-resistance-force gear did not exhibit the sagging characteristic of Type A and B gears. Therefore, it is expected that the weight of the anchor could be reduced by 10–15% when using the proposed low-resistance-force gear.

Despite these promising results, further research is needed to confirm these findings. In particular, field trials need to be conducted to assess the performance of a full-scale gear with reduced resistance force. This step is crucial to verify the effectiveness and practicality of the proposed modifications under actual fishing conditions. These results would greatly contribute to improving the stability and safety of coastal stow net fishing and provide fundamental data for future research associated with this fishing industry.