Greenland Institute of Natural Resources commercial data from the Greenland halibut fishery in Uummannaq fjord; preliminary catch-at-age estimate

Greenland Institute of Natural Resources commercial data from the Greenland halibut fishery in Uummannaq fjord; preliminary catch-at-age estimate

Commercial data for the Greenland halibut fishery in Uummannaq

Northwest Atlantic Fisheries Organization

www.nafo.int Serial No. N7738

NAFO SCR Doc. 26/019

SCIENTIFIC COUNCIL MEETING –JUNE 2026 Commercial data from the Greenland halibut fishery in Uummannaq fjord Rasmus Nygaard1, Henrik Christiansen1 1Greenland Institute of Natural Resources, P.O. Box 570, 3900 Nuuk, Greenland

NYGAARD, R., & CHRISTIANSEN, H. 2026. Commercial data from the Greenland halibut fishery in Uummannaq fjord. NAFO Scientific Council Research Document, SCR Doc. 26/019: 1-17.

Abstract

Although the commercial fishery for Greenland halibut started around 1910 the first available catch statistics from the Uummannaq area are from the 1950s. The fishery is traditionally performed with longlines from small open boats, or dog sledges through a hole in the sea ice. In recent decades a minor part of the catches has also been taken by small vessels using longlines and gillnets. This document presents catch statistics combined from various resources from the Uummannaq fjord. The document includes catch statistics, statistics of commercial sampling effort done by the Greenland Institute of Natural Resources (GINR) and factories, length frequencies in the landings, calculations of mean size in the landings and a preliminary catch-at-age estimation. Also provided are three commercial CPUE indices. Two based on logbooks (one for longline fishery and one for gillnets fishery) and one on factory landings data (longline).

Introduction

The first available catch statistics from the Uummannaq fjord are from 1954. The fishery is traditionally performed with longlines from small open boats, small vessels, or through holes in the sea ice and transported by dog sledge or snowmobile. In the 1980s, small vessels entered the fishery and the use of gillnets increased in the following years. In the late 1990s, the first area limiting regulations were introduced restricting the gillnet fishery to the winter season. Authority to regulate seasons and areas open to the gillnet fishery, was transferred to municipalities in 2004, and areas open to the gillnet fishery expanded since. The minimum mesh size in the gillnets was 110 mm (half meshes or knot to knot) until 2017, when the mesh size was reduced to 95 mm half mesh. Licence requirements were introduced in 1998 and in 2008 TAC and quota regulations were introduced for the inshore fishery. Logbooks have been mandatory for vessels larger than 30ft since 2008. In 2012, the TAC was split in two components with ITQs for vessels and a shared quota for open boats. The ITQ system currently does not specify catch to a certain district which causes a discrepancy between the ITQ and total quota set for each district.

Materials and methods

Input data for catch statistics and CPUE

Recent catch statistics (factory landings and logbooks) are available from a centralized database managed by the Greenland Fisheries and Hunting Control Authority (GFJK). Both logbook (haul by haul) and factory

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www.nafo.int 2 landings (daily individual landings) are reported as individual fishing events containing metadata, such as date, gear, field code or position, effort, fishing period, sorting categories, and more. Data quality has been very good since 2012.

Commercial sampling

Commercial samples are collected by GINR. During surveys or in sampling campaigns factories are visited and the size of the landed fish by species and gear is registered. Due to the logistic challenges in Greenland (size of Greenland and mainly transport by air or sea), sampling the catch is challenging. To ensure sufficient length information from the commercial catches, GINR conducts commercial length measurements in factories during the winter months (Jan-April). An alternative source of length information in the catch are grader data. Graders are automated sorting machines that weigh each fish individually and sort them according to size categories. If extracted, the millions of individual weights can be transformed into length information. Graders typically do not register information on gear. This is, however, not a problem since all fish in the landings provide information, and gear therefore is randomly incorporated into in the length distribution. No grader data has been received from the Uummannaq area since 2021. In 2023-2025, local factory staff have collected the majority of length information

Age-length key (ALK)

Age information is occasionally obtained from commercial landings, but most otoliths in the area are collected through biological surveys with GINR research vessel RV Sanna during summer gillnet surveys.

Logbook CPUE calculation

A general linear model (GLM) with year, month, and boat as factors is applied to the longline and gillnet fishery logbook data since 2008. Only longline sets with more than 200 hooks and gillnets with catches between 0 and 1001 kg/gillnet are included to omit obvious outlier values and limit the influence of potential data errors on the analysis. CPUE observations are log-transformed prior to the GLM analysis. Least-mean square estimates were used as standardized CPUE series. For more information about the standardized logbook CPUE see Riget and Nygaard (2018). In 2022, a new CPUE based on factory landings data from longline fishery calculated in the same way as the logbook CPUE, but from a different data source, was introduced (Bjare and Nygaard, 2022). Another difference is that due to the high number of small boat fishermen and diverse types of fisheries all using the same standard gear (longlines from either logbook vessels, small open boats, or directly from the sea ice) the model uses year, vessel type (vessel, boat, dog sledge or snowmobile) and statistical catch square as factors.

Results

Catches

First available catch statistics are from 1954. Catches increased during the 1980s and peaked in 1999, at more than 8,000 t (Table 1 and Fig. 1). Catches then decreased to around 6,000 but then started to increase and peaked in 2020 with 10,670 t taken in the area. Since then catches have steadily decreased reaching 7,812 t in 2025.

Breakdown of catch

A breakdown of catch by gear and area is provided in Table 2. The fishery in Uummannaq is scattered all over the fjord near settlements (Fig. 2). The area is highly productive with 10 large iceberg producing glaciers.

Size of the landed fish

An overview of number of length measured Greenland halibut by year and gear is shown in Table 3. Due to the logistical challenges in Greenland commercial length information is not available for all months. In most years

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www.nafo.int 3 the sampling covers the three different categories (Uummannaq longline winter, Uummannaq gillnet winter and Uummannaq longline summer). Grader information has not been received from 2022 (Table 4) and due to logistic challenges no sampling was done in the summer of 2022. In Uummannaq there is no major difference between summer and winter fishing grounds and only small differences in the summer and winter length distributions are observed. Only gear is accounted for in the length sampling. Mean individual length in the commercial landings gradually decreased since 1993 with a drastic decrease from 60 cm in 2016 to just above 50 cm in 2023 (Fig. 3), which is also apparent in shifting length frequency distributions (Fig. 4).

Age-length key (ALK)

Age reading of Greenland halibut was suspended from 2011 to 2017 at GINR due to low quality of the age readings and lack of an internationally agreed method. However, in 2017 the ageing was reinitiated. An age- length key (ALK) is currently being constructed for every year back in time. For years prior to 2021, the ALK used to calculate a CAA table, was created using age readings from whole frozen otoliths from all three inshore areas collected from 2008, 2009 and 2010.

Catch-at-age (CAA)

The CAA was constructed with individual year’s ALK from the GINR Uummannaq gillnet survey and based on the new method from 2021 (Table 5). Due to the lack of sufficient length information from the catches, the CAA from Uummannaq is less certain in 2022. The bubbleplot indicates a shift gradual shift towards smaller and younger fish (Fig. 5). In 2025 the catches were dominated by ages 5 to 9.

Factory landings CPUE (longline)

A general linear model (GLM) with year, month, vessel type, and catch area as factors was applied to the longline landings in the factory provided landing slips from 2012 to 2023 (see Bjare and Nygaard, 2022). The new CPUE based on factory landings data consists of more than 10,000 observations in all years and covers

90% all longline fishery (Table 6). The CPUE shows a gradual decrease from 2013 to 2022 and a substantial decrease in 2023-2025 (Fig. 6).

Logbook CPUE (longline)

The CPUE initially increased from 2007 to 2011 but gradually decreased since. The CPUE in 2023-2025 were the lowest observed in the time series (Fig. 6.).

Logbook CPUE (Gillnet)

A general linear model (GLM) with year, month, and boat as factors was applied to the longline fishery logbook data since 2008. Fewer observations are available in 2008, and value for this first year in the time series is thus uncertain.

From 2009, the CPUE gradually increases and peaks in 2013 and again in 2018, whereafter it decreases. Caution should be applied when interpreting the CPUE after 2017 due to the allowed reduction from 110 mm gillnets to 95 mm gillnets leading to a gradual transition to these gillnets selecting fish on average about 10 cm smaller.

Discussion

Although the catches have decreased in the recent 5 years and in general have been high in the recent decade, the catches in numbers of Greenland halibut continue to increase. The fishery is increasingly dependent on younger fish and smaller Greenland halibut. Over the recent decade the main indices for the stock have all gradually decreased concomitant with high catches. Although the CPUEs based on longline fishery are derived from two different data sources, they show a similar trend. The CPUE based on the factory landings starts at a higher level than the logbook based CPUE, but they coincide in 2024-2025 at around 25-27 kg/100hooks. The

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www.nafo.int 4 initial difference in CPUEs between the logbook and the factory-based data could be due to differences in fishing grounds. References

Riget, F. and J. Boje (1989). Fishery and some biological aspects of Greenland halibut (Reinhardtius hippoglossoides) in West Greenland waters. NAFO Sci.Council Studies(13): 41-52.

Riget, F. and Nygaard, R. (2017). An analyses of logbooks of Greenland Halibut Stock Component in NAFO Division 1A Inshore. NAFO SCR 18/023.

Bjare, F. and Nygaard, R. (2022). A new longline based CPUE for Greenland halibut in NAFO division 1A inshore based on factory landing reports. NAFO SCR 12/024.

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Table 1. Catches (t) of Greenland halibut in Uummannaq by gear and year.

Uummannaq

Notes Year Longline Gillnet Catch

1954

16

1955

76

1956

84

1957

31

1958

177

1959

206

1960

No catch statistics ? 1961

No catch statistics ? 1962

No catch statistics ? 1963

No catch statistics ? 1964

403

1965

688

1966

675

1967

593

1968

407

1969

584

1970

326

1971

149

1972

271

1973

No catch statistics ? 1974

No catch statistics ? 1975

309

1976

No catch statistics ? 1977

754

1978

1144

1979

835