유자망 어구에 있어서 어구 자동식별 장치의 현장 적용성 및 침강재 개량에 관한 기초적 연구

Abstract

이 연구는 근해 참조기유자망 어업을 대상으로 어구 자동식별 모니터링 시스템의 적용 가능성을 파악하여 최종적으로 어구 자동식별 장치의 개발과 보급에 대한 기초자료 제공과 근해 참조기유자망 어구의 침강재 개량에 따른 근해 참조기유자망 어구)의 수중 전개 현상을 파악하여 조업 가능성을 검증하고 향후 근해 참조기유자망 어구의 침강재 개량을 통하여 폐그물 발생 저감을 위한 기초자료를 제공하고자 하였으며, 그 결과를 요약하면 다음과 같다.

1. 참조기를 어획하기 위하여 행하여지고 있는 어법은 유자망을 비롯한 안강망, 쌍끌이, 기선저인망 등 다양하지만 참조기 어획량에 있어서 절반 가까이 유자망에 의해 어획되고 있다. 근해 참조기유자망 어업의 성능변화 과정에서 매우 중요한 요소인 선박의 톤수, 선원 수, 어구 재료, 어구 사용량, 어로 장비, 양망기 등은 현재까지 매우 발달 되어왔으며, 어구 사용량 또한 매우 증가하였다.

2. 2021년을 기준으로우리나라 근해 유자망 어선의 등록 척수는 총405척이다.이중 전라남도가 148척(36.54%)으로 가장 높았고 그 다음으로는 제주도가99척(24.44%), 울산이 26척(6.42%)이었다.

3. 우리나라 근해 자망어업 생산량은 2016년이 29,937 톤으로 가장 낮았고, 이듬해부터 서서히 증가하다가 2020년에 52,075 톤으로 가장 높게 나타났으며, 우리나라 근해 참조기유자망 어업의 연간 생산량은 2017년이 12,347톤으로 가장 낮았고, 이듬해부터 서서히 증가하다가 2013년에 24,506톤으로 가장 높게 나타났으며, 2014년에는 17,302톤으로 약 30% 가량 감소하는 경향을 보였다.

4. 유자망 어업인을 대상으로한 설문조사에서 1회 조업 시 그물 파망(그물의 찢어짐폭 수는 40~50폭이 73.1%를 차지하였고, 그다음으로는 30~40폭 및 50~60폭이 각각 11.5% 순으로 나타났으며, 1항차 조업 시 어구 수리와 교체량은 250~300폭이 69.2%를 차지하였고, 그 다음으로는 300~350폭이 19.2% 순으로 나타났다.

5. 모형유자망 어구에 대한 실험 횟수별 평균 이동속도는 1회차 및 2회차 시험의 경우 2.08m/s(GPS-1), 2.08 m/s(GPS-2)로 나타났으며, 3회차 및 4회차 시험의 경우 0.23 m/s(GPS-1), 0.24 m/s(GPS-2)로 나타났다. 또한, GPS 측정 결과에 있어서 모형유자망 어구의 이동 궤적에 따라 모형유자망 어구의 최대길이(196m) 기준 약 19.6(5%∼10%) 범위로 양쪽 간격이 매우 좁아지는 현상이 나타났다.

6. 모형유자망 어구의 전개수심은 1회 실험의 경우 그물의 첫 번째 뜸줄과 발줄 부분의 수심 측정계(D-1, D-2) 및 끝부분에 부착한 뜸줄과 발줄 부분의 수심 측정계(D-3, D-4)와 수심 차이가 모형 유자망 어구의 설 높이(약 3m)보다 크게 나타났다.

7. 어구 자동식별 장치를 부착한 현장의 근해 참조기유자망 어구에 대한 현장시험 결과 투망 평균 소요 시간은 약 90.6분이었으며, 양망 평균 소요 시간은 약 631분이었다. 유자망 어구의 이동 거리는 각각 회차별로 11,500m, 10,300m, 2,033m 순으로 나타났다.|This study is aimed at providing basic data for development and supply of automatic fishing gear identification devices by identifying the applicability of automatic fishing gear identification monitoring system for off-shore small yellow croaker drift gill nets. In addition, this study intends to verify the operability of off-shore small yellow croaker drift gill nets by identifying their underwater deployment pattern in line with improvement of sedimentation materials of the nets. The purpose of this study is to provide basic data for waste net reduction through improvement of sedimentation materials of off-shore small yellow croaker drift gill nets. The findings are as follows.

1. There are various fishing tools for catching small yellow croakers, such as drift gill net, stow net, lage pair-trawl and pair-trawl. Nearly half of small yellow croakers are, however, caught through drift gill nets. The key factors of their performance change are tonnage of ships, the number of crew members, fishing gear materials, fishing gear usage, fishing equipment, and haulers, which have improved substantially.

2. As of 2021, the number of registered fishing boats with off-shore drift gill nets in Korea is 405. It includes 99 ships (24.44%) in Jeju Island, 148 ships (36.54%) in Jeollanam-do, and 26 ships (6.42%) in Ulsan.

3. Korea's fishing production with off-shore gill net was the lowest at 29,937 tons in 2016 and has gradually increased since the following year. Then it reached the highest level at 52,075 tons in 2020. Korea's annual fishing production with off-shore small yellow croaker drift gill net was the lowest at 12,347 tons in 2017, and has gradually increased since the following year. It reached the highest level at 24,506 tons in 2013, and stood at 17,302 tons in 2014, down 30% from the previous year.

4. In a survey of drift gill net fishermen, 40-50 width accounted for 73.1% of the net breaks (net tearing) during an operation, followed by 30-40 width and 50-60 width at 11.5%, respectively. 250-300 width accounted for 69.2% of fishing gear repairs and replacements during the first operation, followed by 300-350 width at 19.2%.

5. The average moving speed of the model drift gill net in each test is as follows. 2.08 m/s (GPS-1) and 2.08 m/s (GPS-2) in the 1st and 2nd tests. 0.23 m/s (GPS-1) and 0.24 m/s (GPS-2) in the 3rd and 4th tests. GPS measurement results showed that the gap between the two sides was very narrow in the range of 19.6 (5%-10%), based on the maximum length (196m) of the model drift gill net, in line with the movement trajectory of the gear.

6. The deployment depth of the model drift gill net showed the following result in a test. The difference in depth between the depth gauge (D-1, D-2) of the first float line and sinker line of the net, and the depth gauge (D-3, D-4) of the float line and sinker line attached to the ends was greater than the model drift gill net height (around 3m).

7. A field test on an off-shore small yellow croaker drift gill net equipped with an automatic fishing gear identification device revealed that the average casting time was 90.6 minutes. The average hauling time was 631 minutes. The moving distance of the drift gill net was 11,500m, 10,300m, and 2,033m, respectively, in the order of each round.

8. A field test on an off-shore small yellow croaker drift gill net equipped with an automatic fishing gear identification device showed that all B-type underwater transmitter prototypes had normal operations. After the field test, A-type underwater transmitter prototypes were found to be defective mechanically and electronically. It indicates that B-type underwater transmitter is a suitable type, and stick-type receiver detachable from the buoy flag pole was found to be suitable. The field test found that the communication status between the wireless node for fishing boat and the receiver was normal, based on the partial location records by time.

9. Measurement of sedimentation depth of the off-shore small yellow croaker drift gill net led to the following result. In each round, the net sank in a gentle straight line immediately after casting and then sank in a rapidly-developed horizontal direction after 40 minutes on average. In the 1st field test, the first and middle parts of the net showed a difference of 12m in the highest water depth when they reached underwater. It confirmed that the rest of the nets except for the last net of the drift gill net were deployed in an unstable fashion underwater for the most part.

10. Following the development of automatic fishing gear identification monitoring system, 76.9% of the respondents stated "Average" when asked about their intention to use it, followed by "Necessary" at 7.7% and "Unnecessary" at 7.7%. As for the reason why the automatic fishing gear identification monitoring system is unnecessary, 50% of the respondents replied they were satisfied with the electronic buoy they were using, followed by "financial burden" at 31.8% and "difficulties with repair and management" at 18.2%. When they were asked whether they would use the automatic fishing gear identification monitoring system, if it was cheaper than the electronic buoy they were using, 61.5% of the respondents gave positive answers.

11. In the field test, the improved sinker was called “floor line.” the interaction formula as to the FS between the float line and sinker line, and the SFL between the sinker line and floor line of the drift gill net with improved sediment is as follows.

FS=depth(x)+c ································································(1)

SFL=depth(x)+c ································································(2)

12. Coefficient of determination values for FS were in the range of 26.4% in the 4th test and 0.1% in the 6th test. Coefficient of determination values for SFL were in the range of 0.0% in the 4th test and 74% in the 6th test. values indicate that there was a low correlation between the depth change and FS in all of the seven sea tests. Despite the similar results in the changes of depth and SFL versus the depth and FS, the 5th and 6th sea tests showed a very high correlation between the changes in depth and SFL with values of 74% and 43%, respectively.

13. Therefore, as the value approaches 1, the changes in depth have a stronger effect on the FS and SFL of off-shore small yellow croaker drift gill nets with floor lines attached. As the value is closer to 0, the effect of floor lines on the FS and SFL of off-shore small yellow croaker drift gill nets is more insignificant.

14. In terms of net replacement amount due to breakage (net tearing) of off-shore small yellow croaker drift gill net, it was identified through 200 width for those with floor lines attached and the remaining 300 width for conventional nets. The off-shore small yellow croaker drift gill nets with floor lines attached showed a very low replacement rate of 2.4% of the total net amount.