2006/824 l 15/12/2009 2006/824 l 27/01/2010
Review of fisheries biology for ribaldo
Review fisheries biology for ribaldo (Mora moro)
Lauren Veale and Kyne Krusic‐Golub
Not for citation without permission
January 2010
Department of Primary Industries
Review of fisheries biology for ribaldo (mora moro)
Published: Fisheries Research Branch Department of Primary Industries, Queenscliff PO Box 114, Queenscliff, 3225 Victoria
General disclaimer This publication may be of assistance to you but the State of Victoria and its employees do not guarantee that the publication is without flaw of any kind or is wholly appropriate for your particular purposes and therefore disclaims all liability for any error, loss or other consequence which may arise from you relying on any information in this publication. Copyright © The State of Victoria, Department of Primary Industries, 2010.
This publication is copyright. No part may be reproduced by any process except in accordance with the provisions of the Copyright Act 1968. Authorised by the Victorian Government, 2a Bellarine Highway, Queenscliff 3225 Printed by DPI Queenscliff, Victoria Preferred way to cite: Veale, L., and Krusic‐Golub, K. (2010). Review of fisheries biology of ribaldo (Mora moro). Report to Australian Fisheries Management Authority. Department of Primary Industries, Queenscliff. p15
ISSN 1449‐2520 ISBN 978‐1‐74199‐554‐1
Review of fisheries biology for ribaldo (mora moro) ii Executive Summary
Ribaldo (Mora moro) are a deep‐sea cod caught on bottom long‐lines and as a bycatch of deepwater trawling in the Southern and Eastern Scalefish and Shark fishery (SESSF). They are a companion species with ling in the auto long‐line (ALL) sector and of low value to the commonwealth trawl (CT) sector. Recent catches in the SESSF averaged 174 t prior to the induction of a 100 t Total Allowable Catch (TAC) in 2005. The following year, discard rates increased from 14 to 28%, prompting Australian Fisheries Management Authority (AFMA) to raise the TAC to 165 t in 2006. Very little information on the life history and biology of this species is currently available. In Australia information on age, growth and mortality is limited to approx 700 age estimates from the SESSF. The lack of ages for this species was discussed at the Slope Assessment Group (SlopeAG) meeting held in May 2006. This was seen as a component of the stock assessment process that could be improved relatively easily through the age estimation of additional species. The SlopeAG also recommended undertaking a review of the fisheries and biological information to determine future research priorities for this species. This report presents an overview of the ribaldo fishery within the SESSF, reviews the information on growth and reproduction that is currently available, and indicates research priorities required for improved assessment of this species.
Review of fisheries biology for ribaldo (Mora moro) iii Table of Contents
Executive Summary...... iii
Introduction...... 1 Objectives...... 1
Taxonomy...... 1 Classification ...... 1 Morphology...... 1
Distribution ...... 2
Fisheries...... 4 Ribaldo in Australia ...... 4 Ribaldo in New Zealand...... 6 Ribaldo in the Mediterranean Sea ...... 7
Previous research...... 7 Size structure and sex ratio...... 7 Age/Growth and Length‐Weight Relationships...... 9 Reproduction and Life History...... 10 Mortality ...... 11 Diet ...... 12 Stock Structure ...... 12
Future research needs ...... 12
Acknowledgments ...... 13
References ...... 14
Review of fisheries biology for ribaldo (Mora moro) iv List of Tables Table 1. Generas of the moridae family, examples of species within each genera and relative distribution and maximum size...... 3 Table 2. Maximum and mean lengths of female/male ribaldo and other morids from various authors...... 8 Table 3. Age and growth information for ribaldo and other morids estimated by various authors...... 10 Table 4. Reproduction and spawning information for ribaldo and other morids, collected by various authors...... 11
List of Figures Figure 1. Ribaldo (Mora moro) ...... 2 Figure 2. Distribution of ribaldo with corresponding probability of occurrence...... 2 Figure 3. Map of the Southern and Eastern Shark and Scalefish Fishery ...... 4 Figure 4. Annual retained and discarded catch for ribaldo (1994–2006) from different sectors of the SESSF. (Source: Koopman, unpublished)...... 5 Figure 5. Standardised CPUE (kg/km tow) of ribaldo for period 1994–2005. Note: Data collected by onboard observers where catch refers to total (retained and discarded)...... 5 Figure 6. Ribaldo CPUE (kg/km) at different depths for period 1994‐05. Error bars represent 95% confidence intervals. Note: Data collection by onboard observers where catch refers to total (retained and discarded)...... 6 Figure 7. Length frequency of ribaldo for period 2004–06, using species stock assessment data from the SESSF...... 7 Figure 8. Mean length (±SE) and size range of ribaldo (SESSF) according to depth, measured by onboard ISMP observers on trawl and non‐trawl vessels in the SESSF (1985–06)...... 9 Figure 9. Age frequency of ribaldo for period 2004–06...... 9
Review of fisheries biology for ribaldo (Mora moro) v
Introduction
Ribaldo (Mora moro) are a recently exploited deep‐sea cod caught as bycatch by bottom long‐line and bottom gear in Australia, New Zealand, Iceland, the Mediterranean Sea and the North Atlantic. Found at depths 300 to 2,500 m, ribaldo have been known to reach lengths of 80 cm and live to more than 57 years. Despite their wide distribution and increasing economic importance, information on the biology, reproduction and population dynamics of ribaldo remain largely unknown. This report summarises biological information available for ribaldo and provides future research priorities to assist in the development of sustainable management practices for this species. Objectives 1. Summarise available biological and fisheries information for ribaldo 2. Determine research priorities that are required for the sustainable exploitation of this species
Taxonomy Classification Order: Gadiformes (cods and hakes) Family: Moridae (codlings and deepsea codfishes) (Moreau, 1881) Genus: Mora Species: Mora Moro (Risso, 1810)
Information on identification for this species is readily available (Cohen et al. 1990). Ribaldo belong to the family Moridae, where there are 111 species in 18 genera. Morids occur throughout the world and can grow to 90 cm long (table 1). Ribaldo are the only species in the genus Mora, and are one of the larger species of morids. Other common names include ghost cod, googly‐eyed cod and common mora.
Morphology Morphological features that distinguish ribaldo from other morids, include: • two anal fins • large eyes • a well‐forked caudal fin • easily lost scales • grey‐pink colourings along the lateral line, a white belly and reddish fins.
Review of fisheries biology for ribaldo (Mora moro) 1
Figure 1. Ribaldo (Mora moro) (Source: McMillan and Hart 1998)
Distribution Ribaldo are widely distributed, showing bathymetric distribution along the middle to upper continental slopes. They are found worldwide in temperate seas at depths of 300 –2,500 m. As deepwater research and exploratory surveys are limited, global distribution of ribaldo is largely based on fisheries catches. In the Southern Hemisphere, ribaldo occur at latitudes between 32 and 53°S where they are distributed throughout southern Australia, south Madagascar and the west coast of Chile (Cohen et al. 1990). In the Northern Hemisphere they are known to occur from Iceland to West Africa, including the west Mediterranean (Cohen et al. 1990) (figure 2). Ribaldo are known to feed on fishes, crustaceans, molluscs and other invertebrates as well as food of terrestrial origin, including garbage (Froese and Pauly 2004).
Figure 2. Distribution of ribaldo with corresponding probability of occurrence. (Source: Froese & Pauly 2004)
Review of fisheries biology for ribaldo (Mora moro) 2
Table 1. Generas of the moridae family, examples of species within each genera and relative distribution and maximum size.
Genus No. E.g of species and Distribution Max species common name size
Antimora 2 Blue Antimora All oceans except North Pacific 75 cm (A. rostrata) 350‐ 3,000 m.
Auchenoceros 1 Ahuru Southeast Pacific: east coast New Zealand. 13 cm (A. punctatus) 5‐ 420 m. Eeyorius 1 Tasmanian Coldling Indo‐Pacific: Western Australia, Tasmania, Victoria. 26 cm (E. hutchinsi) 8‐12 m.
Eretmophorus 1 E. kleinenbergi Mediterranean Sea. 9 cm 30‐ 500 m.
Gadella 13 Beardless codling (G. Western Atlantic 23 cm imberbis) 200‐ 800 m.
Guttigagus 7 Tadpole Cod Oceanic islands of New Zealand, Mid South Atlantic. 18 cm (G. globosus) 1200‐ 1600 m.
Halargyreus 1 Slender codling All oceans. 55 cm (H. johnsoni) 450‐ 3000 m
Laemonema 17 Shortbeard codling Western Atlantic. 27 cm (L.barbatulum) 50‐ 1620 m
Lepidion 9 Small‐headed cod Tasman Sea, Bass straits, New Zealand. 48 cm (L. microcephalus) 750‐ 1,000 m Lotella 6 Rock Cod South Eastern Australia, Tas, Great Australian Bight and 50 cm (L. rhacina) New Zealand coast. 10‐ 90 m. Mora 1 Ribaldo 80 cm (M. moro) Notoptycis 2 Dwarf codling Southeast Pacific, Southwest Atlantic. 24 cm. (N. marginate) 1200 m.
Physiculus 42 Skulpin Southeast Atlantic: St. Helens Island. 30 cm (P. helenaensis)
Pseudophycis 3 Red Colding South Aus, Tas, New Zealand. 90 cm. (P. bachus) 700 m.
Rhynchogadus 1 R. hepaticus Eastern Atlantic 10 cm
Salilota 1 Tadpole codling Southwest Pacific and southwest Atlantic. 50 cm (S. australis) 30‐ 1000 m. Svetovidovia 1 S.lucullus Northeast Atlantic 50 cm
Tripterophycis 2 Grenadier cod Mid South Atlantic, South Ocean 35 cm. (T. gilchristi) 100‐ 1000 m.
(Source: Froese and Pauly 2004)
Review of fisheries biology for ribaldo (Mora moro) 3 Fisheries Ribaldo in Australia Ribaldo are captured as a companion species with pink ling (Genypterus blacodes) in the auto long‐line sector and as a low‐value species in the trawl sector of the South Eastern Shark and Scalefish Fishery (SESSF) including areas of the Great Australian Bight (GAB) (figure 3).
Trawl exclusion zone East Coast Deepwater Sector Commonwealth GAB Trawl Sector Commonwealth Trawl Sector South Australia Coastal Waters Sector Limit of coastal waters Limit of Australian Fishing Zone (200nm)
Figure 3. Map of the Southern and Eastern Shark and Scalefish Fishery (Source: AFMA 2005).
Due to declining catches of target species (specifically pink ling) since 1999, fishers have steadily increased the retained proportion of landed ribaldo (Figure 4). In 2004, significant catch increases raised concerns over the sustainability of ribaldo and in response; the Australian Fisheries Management Authority (AFMA) imposed a precautionary Total Allowable Catch (TAC) of 100 t. The following year discard rates increased from 14 to 28%, prompting AFMA to raise the TAC to 165 t in 2006. Prior to 2002, ribaldo were predominantly caught from the commonwealth trawl sector of the SESSF (Figure 4). Recent increases of ribaldo catch have mainly been due to the development of demersal auto long‐lining since 2002. According to standardised catch per unit of effort (CPUE) (kg/km‐all sectors) collected from observer data for years 1995–2005, ribaldo abundance has declined since 1999 (Figure 5). In addition, CPUE trends also suggest ribaldo are most abundant at depths 700–900 m (Figure 6).
Review of fisheries biology for ribaldo (Mora moro) 4 Ribaldo are currently managed under a Recommend Biological Catch (RBC) based tier 4 harvest control rule which employs trends in catch rates.
250000 Non-trawl Discards Trawl Discards 200000 Non-trawl Catch State Catch 150000 Commonwealth Catch
100000 Catch (kg) Catch 50000
0 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 Year
Figure 4. Annual retained and discarded catch for ribaldo (1994–2006) from different sectors of the SESSF. (Source: Koopman, unpublished).
5
4
3
2 (Kg/km)
1 Standardized CPUE 0 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 Year
Figure 5. Standardised CPUE (kg/km tow) of ribaldo for period 1994–2005. Note: Data collected by onboard observers where catch refers to total (retained and discarded). (Source: Modified from Walker et al. 2007).
Review of fisheries biology for ribaldo (Mora moro) 5
CPUE (kg/km)
0 100 200 300 400 500 600 700 800 900 10
Depth (m)
Figure 6. Ribaldo CPUE (kg/km) at different depths for period 1994‐05. Error bars represent 95% confidence intervals. Note: Data collection by onboard observers where catch refers to total (retained and discarded). (Source: Modified from Walker et al. 2007). Ribaldo in New Zealand In New Zealand, ribaldo are caught on bottom long‐lines and as bycatch during target trawling for hoki (Macruronus novaezelandiae), orange roughy (Hoplostethus atlanticus) and ling (Genypterus blacodes). In recent years (since the 1990s), most reported catch has been taken by long‐line at depths 700–1000 m. In the 1970s catches of up to 4920 t per year were reported by Japanese and Korean long‐liners (McMillian and Hart 1998). Ribaldo was introduced into the Quota Management Scheme (QMS) from October 1999 under the Low Knowledge Stocks, as there was insufficient information on stock status relative to Maximum Sustainable Yield. In 2004–05 the TAC (for all QMAs) of 1200 t was exceeded by 22 t (Ministry of Fisheries 2006). In reflection of recent landings being well above original TACs, the Ministry of Fisheries increased quotas in the main fishing areas (6 & 7) for the 2006–07 season to 1334 t. Following the inclusion of ribaldo into the QMS, the first stock assessment was conducted in 1998. This involved resource surveys where preliminary catch‐rate information, relative abundance, length‐ frequency, length‐weight relationship, reproduction and spawning data were collected (McMillian and Hart 1998). There have been no new data since 1998 to change that assessment. It is unknown whether recent catches are sustainable or whether the current TACs allow stocks to move towards a size that supports maximum sustainable yields (Ministry of Fisheries 2006). To address this uncertainty, the Ministry of Fisheries has proposed for an updated stock assessment of ribaldo to be undertaken. This research project is considered to be of high priority given that TACs have increased in the two main fisheries (QMAs 6 &7) in recent years, and ribaldo are regarded as an important bycatch species in New Zealand and are potentially slow growing (Ministry of Fisheries 2007). Other commercially important morids caught in New Zealand waters include the red cod (Pseudophycis bachus), the deepwater slender cod (Halargyreus johnsoni) and the less abundant deepwater violet cod (Antimora rostrata) (Ministry of Fisheries 2006). Red cod in particular are caught in substantial quantities, with annual landings reaching 18 000 t (Horn 1996). In comparison to ribaldo, red cod is regarded to be short‐lived (live to 4 yrs) and fast growing (refer to Table 3), allowing it to support productive fisheries in New Zealand.
Review of fisheries biology for ribaldo (Mora moro) 6 Ribaldo in the Mediterranean Sea Ribaldo occur in the deep waters of the Mediterranean Sea where they are most abundant between 1000– 1450 m (Carrasson et al. 1997). Two other morids occur throughout this zone; the Mediterranean codling (Lepidion lepidion), which is endemic to the Mediterranean and most abundant at these depths; and Lepidion guentheri, a rare species. In 2002, ribaldo were not exploited in the Mediterranean Sea, as commercial trawling was restricted to a depth shallower than 700 m (Rotllant et al. 2002). Although no publications since then could be found, Rotllant et al. (2002) suggested that the development of this fishery was inevitable, due to declining traditional inshore fisheries and improved trawling systems. Prior to establishing a new fishery and in order to avoid over‐exploitation, authors (Rotllant et al. 2002) insisted that more biological data, especially in reproduction was needed.
Previous research In 1985, Gordon and Duncan analysed the biology of three morid species (Mora moro, Lepidion eques and Halargyreus johnonii) in the deep‐water of the Rockall Trough in the North Atlantic. This study focused on reproduction, fecundity, age composition and changes in abundance and length composition with depth. A similar study in 2001 conducted by Rotallant et al. (2002) investigated the reproductive biology of three Mediterranean gadiform species (Mora moro, Phycis blennoides, and Lepidion lepidion). Size structure and sex ratio Ribaldo are considered one of the largest species of the upper and mid slope morids (Gordon & Duncan 1985) reaching a maximum size of 77 cm and 78 cm for males and females, respectively. The maximum and mean lengths of male and females from various moridae species (including ribaldo) are summarised in Table 2. Sexual dimorphism is evident in ribaldo with females constituting the majority of larger size classes (Figure 7). Studies in New Zealand and the Mediterranean show sex ratios favour females (McMillan and Hart 1998; Rotllant et al. 2002). Preliminary data collected by the Integrated Scientific Monitoring Program (ISMP) working on vessels operating in Australia’s SESSF, indicate no obvious multi‐modal progressions in terms of length or age (Figure 8 & 9).
70
60 Females 50 Males 40
30 Frequency 20
10
0 10 15 20 25 30 35 40 45 50 55 60 65 70 77 Length (cm)
Figure 7. Length frequency of ribaldo for period 2004–06, using species stock assessment data from the SESSF. (Source: CAF unpublished).
Review of fisheries biology for ribaldo (Mora moro) 7 Onboard ISMP and logbook data from the SESSF indicate the mean length of ribaldo may increase with depth (Figure 8). Trawl surveys in the Mediterranean also support this trend (Rotllant et al. 2002).
Table 2. Maximum and mean lengths of female/male ribaldo and other morids from various authors Species Author Max Length Mean Lengths
Mora moro CAF unpublished M: 77 cm M: 46 cm
F: 78 cm F: 53 cm
Mora moro McMillan & Hart 1998 M: 60 cm (FL)
(New Zealand) F: 79 cm (FL)
Mora moro Rotllant et al. 2002 (Mediterranean Sea) M/F: 53 cm
Lepidion eques Magnusson 2001 M/F: 49 cm M: 29.0 cm
(Iceland) F: 28.9 cm
Lepidion eques Gordon & Duncan 1985 M/F: 31 cm (SL) M: 39 cm (SL)
(North Atlantic) F: 34 cm (SL)
Antimora rostrata Magnusson 2001 M/F: 66 cm M: 32.8 cm
(Iceland) F: 29.0 cm
Antimora rostrata Gordon & Duncan 1985 M: 37 cm (SL)
(North Atlantic) F: 53 cm (SL)
Halargyreus johnsonii Gordon & Duncan 1985 M: 29 cm (SL)
(North Atlantic) F: 34 cm (SL)
Phycis blennoides Rotllant et al. 2002 (Mediterranean Sea) M/F: 62 cm
Lepidion lepidion Rotllant et al. 2002 (Mediterranean Sea) M/F: 36 cm Notes: Lengths refer to total length, unless stated otherwise.
Review of fisheries biology for ribaldo (Mora moro) 8 80 70 60 49-72 50 40-72 33-76 36-76 46-72 32-71 36-69 29-69 28-88 25-90 40 30 20 Size Class (TL, ClassSize cm) 10 0 200 300 400 500 600 700 800 900 1000 1100 Depth Category (m)
Figure 8. Mean length (±SE) and size range of ribaldo (SESSF) according to depth, measured by onboard ISMP observers on trawl and non‐trawl vessels in the SESSF (1985–06). (Source: AFMA unpublished) Age/Growth and Length‐Weight Relationships The Central Ageing Facility (CAF), based at the Department of Primary Industries (DPI) Queenscliff Centre, has provided approximately 700 unvalidated age estimates from otoliths collected from commercial vessels operating in the SESSF between 2004–2006. Age estimates range between 5–57 years and indicate age at full recruitment of 17 years (Figure 9). This is considered to be a preliminary estimate, given the short time‐series of age data. No other age estimates for ribaldo are available.
80 70 60 Females 50 Males 40 30 Frequency 20 10 0 5 101520253035404654 Age ( yr s)
Figure 9. Age frequency of ribaldo for period 2004–06. (Source: CAF unpublished).
Review of fisheries biology for ribaldo (Mora moro) 9
Table 3 summarises length‐weight and growth parameters for ribaldo and other morid species that have been estimated by various authors from Australia and elsewhere.
Table 3. Age and growth information for ribaldo and other morids estimated by various authors.
Species Author Length‐length Length‐weight Growth parameters (both sexes) (W= aSLb ) (Lt =L∞ (1‐e(‐k(t‐to)) )
Mora moro Veale, in prep; TL = a + bSL M: a=0.0079,b=3.157 M: L∞= 46.5, k= 0.088, t0= ‐1.9, a=‐0.301, b=1.1108 F: a=0.0062, b=3.225 F: L∞= 61.3, k= 0.105, CAF unpublished TL = a + bFL t0= ‐0.788 a=0.033, b=1.0293
Mora moro McMillan & Hart M: a=0.0531, b=3.300 1998 F: a=0.0357, b=3.294 (New Zealand)
Lepidion Magnusson 2001 M: a= 0.008, b=3.586 M/F: L∞= 47.50, eques (Iceland) F: a= 0.001, b=3.498 k= 0.103, t0= ‐1.051.
Antimora rostrata Magnusson 2001 M: a=0.001, b=3.519 M/F: L∞= 61.37, (Iceland) F: a=0.001, b=3.605 k= 0.089, t0= 0.205.
Antimora rostrata Gordon & Duncan M/F: a=0.0019, b=3.47 1985 (North Atlantic)
Pseudophycis Horn 1996 M: a=0.0145, b=2.892 M: L∞=68.5, k=0.47, t0=0.06, bachus F: a=0.0097, b=3.00 F: L∞=76.5, k= 0.41, t0= ‐0.03
Reproduction and Life History No reproductive studies of ribaldo have been undertaken in Australia. Overseas studies (Rotllant et al. 2002) indicate ribaldo are iteroparous; however, it is unsure whether this species are all‐at‐once or batch spawners (Rotllant et al. 2002). In the Mediterranean, Rotllant et al. (2002) observed mature females all‐ year‐round except in summer and mature males in autumn and spring suggested a quasi‐continuous reproductive pattern and possible batch‐spawning event in females. Authors believe the physical constancy in the deep‐sea of the Mediterranean Sea may enable deeper dwelling gadiforms such as ribaldo to lengthen their reproductive season. Comparatively shallower studied gadiforms (Phycis. blennoides) were found to show seasonal reproductive patterns. Magnusson (2001) suggests other morids may also spawn all‐year‐round (Table 5). Another study in the Mediterranean Sea (Cohen 1986) indicated ribaldo were winter to early spring spawners. Preliminary stock assessments in New Zealand attempted to analyse length‐at‐maturity for ribaldo; however, too few gonad stage data were collected (47 females; 27 males). Most individuals were resting or pre‐vitellogenic with only one female showing hyaline eggs. A small group of maturing individuals were observed in orange roughy spawning boxes during a fisheries survey suggesting winter to spring spawning (McMillan and Hart 1998). Histological studies of three gadiforms (Mora moro, Phycis blennoides, and Lepidion lepidion) by Rotllant et al (2002) confirm biological similarity between species. Gonads were internal, longitudinal, paired and laid alongside the gas bladder. This study found females to reach sexual maturity at a larger size than males (Table 4). Gordon and Duncan (1985) in the North Atlantic have conducted the only study to determine estimates of fecundity. Although only 3 mature females were collected, gonadsomatic indices and relative
Review of fisheries biology for ribaldo (Mora moro) 10 fecundities were estimated for two females, both of 58 cm (SL) (Table 4). Results suggest that ribaldo may have a high fecundity. The early life history of ribaldo is largely unknown. In New Zealand, individuals have been captured in plankton nets in the upper 200m of the water column over bottom depths of about 1000m in the Chatham Rise (McMillan and Hart 1998).
Table 4. Reproduction and spawning information for ribaldo and other morids, collected by various authors.
Species Author Sexual Maturity Spawning Fecundity/ GSI period Mora moro McMillan and Hart 1998 Winter (July– August) (New Zealand)
Mora moro Rotllant et al. 2002 M: 32 cm Year round except (Mediterranean Sea) summer F: 34 cm
Mora moro Gordon and Duncan 1985 58 cm (SL) fish:
(North Atlantic) GSI: 12.3 – 21.4; and
Fecundity: 3,366,772 – 2,160,840
Lepidion Magnusson 2001 (Iceland) M: 18 cm Year round except lepidion summer F: 20 cm
Lepidion Magnusson 2001 (Iceland) 50% mat point Year round eques M: 33.2 cm
F: 30.2 cm
Approx, 8– 9 yrs.
Antimora Magnusson 2001 (Iceland) 50% mat point Autumn to Winter rostrata M: 45.1 cm
F: 42.1 cm
Approx, 8‐9 yrs.
Antimora Gordon and Duncan 1985 F: 24 cm (SL) 25 cm (SL): 3424 rostrata (North Atlantic) 33 cm (SL): 110, 023
Phycis Rotllant et al. 2002 M: 19 cm Autumn blennoides (Mediterranean Sea) F: 20 cm Notes: Lengths refer to total length, unless stated otherwise. Mortality Mortality estimates for ribaldo are only available from Australian preliminary stock assessments for period 2004‐06. Age data have produced initial estimates of natural (M) and total (Z) mortality of 0.08 yr‐ 1 and 0.18–0.21 yr‐1 respectively (depending on the range of ages included in the analyses). These predict an exploitation rate (F/M ratio) of 1.14–1.50, suggesting ribaldo populations in Australia are relatively unproductive and unlikely to sustain high levels of fishing pressure.
Review of fisheries biology for ribaldo (Mora moro) 11 McMillan and Hart (1998) in the New Zealand fisheries assessment report predicted ribaldo have an M estimate similar to other Gadifom fishes. Considering estimates of M for Red Cod (0.76), Hake (0.2–0.22) and Hoki (0.25–0.30) (Annala and Sullivan 1997), McMillan and Hart (1998) suggested ribaldo M to be 0.2–0.3. Diet A study by Carrasson et al. (1997) on the western Mediterranean slope looked at the feeding strategies of deep‐water morids, including ribaldo, the Mediterranean codling (Lepidion lepidion) and Lepidion guentheri. Due to an elevated number of specimens with everted stomachs, only 3 collected specimens were suitable for analysis. Food items consisted of decapods, cephalopods and fishes, suggesting that the diet of ribaldo mainly consists of epibenthic (living on, or attached to a substrate surface) and suprabenthic (live close to the bottom) prey. Carrasson et al. (1997) surmised that ribaldo are likely to have high‐energy requirements, as indicated by their high fecundity (Gordon and Duncan 1985). In addition, the decline of resources beyond 1200–1400 m could account for the lower abundance of ribaldo at increasing depths, as observed in this study. Stock Structure No studies on the stock structure of ribaldo have been undertaken in Australia or elsewhere. Separate stocks, however, have been suggested based on natural boundaries such as landmasses and the main areas of capture. In Australia, ribaldo are currently managed under the assumption that one stock exists. The SlopeRAG (2006) have considered several stocks including eastern and western Bass Strait and the GAB. In New Zealand, a Working Group has agreed on five fish stocks for ribaldo based on fisheries catches (Ministry of Fisheries 2006).
Future research needs The current project aims to improve the management of ribaldo through obtaining robust estimates of fishing mortality and natural mortality. As the fishery for ribaldo is recently developed, there is an opportunity to obtain accurate mortality estimates using data from virgin or under‐exploited stocks. The project will facilitate an increased understanding of the age structure of ribaldo and additionally improve understanding of growth and contribute to the time‐series data. In order to increase the precision of age estimates, future research needs to investigate age validation techniques for this species. A recently developed project in New Zealand (Ministry of Fisheries 2007) proposes to validate the use of otolith zone counts as a method of estimating the age of ribaldo. This is particularly important, given that ribaldo otoliths are relatively complex and the species appears to have a high longevity. Future research needs to focus on ribaldo reproduction and fecundity to help determine their productivity and resilience to over‐fishing. A preliminary study, that aims to provide an indication of the time of spawning, age/length of maturity and fecundity of ribaldo is currently under way. Future studies on ribaldo stock discrimination would assist authorities in developing the most appropriate management strategies for this species. This may involve genetic identity and DNA studies of stocks, or other methods such as otolith microchemistry. No attempt has been made to estimate the biomass of ribaldo stocks in Australia or elsewhere. This would require detailed and extensive fisheries‐independent research surveys, given the apparent wide distribution of ribaldo and the small number of specimens captured in single trawl shots. The relevant survey areas and strata, appropriate sampling methods and gear would need to be considered in producing comparable abundance estimates. Acoustic surveys may also be useful in estimating stock biomass, given that other deepwater species such as orange roughy (Hoplostethus atlanticus) and roundnose grenadier (Coryphaenoides rupestris) are considered acoustically reflective (Large et al. 2003). Finally, it would be useful to conduct diet studies on ribaldo to identify their niche in ecosystems and help predict their environmental and spatial distribution.
Review of fisheries biology for ribaldo (Mora moro) 12 Preliminary studies indicate ribaldo have a high longevity, low natural morality and slow growth rate, suggesting populations may be unproductive and vulnerable to over‐fishing. Future research to obtain more information on ribaldo will allow authorities to implement appropriate management strategies that ensure the species long‐term sustainability and allow industry to fully utilise ribaldo as a sustainable resource.
Acknowledgments The authors would like to acknowledge AFMA for their support in funding this review and further research. Fisheries research Branch staff Matthew Koopman for suppling Catch and effort data. The CAF for supplying age and length data
Review of fisheries biology for ribaldo (Mora moro) 13 References
Annala, J., and Sullivan, K. 1997 ‘Report from the Fishery Assessment Plenary, May 1997: Stock assessment and yield estimates. p.381. (Unpublished report held in NIWA library, Wellington) in McMillian, P & Hart, A. 1998. Summary of biology and commercial landings, and a stock assessment of ribaldo, Mora moro (Risso, 1810), in New Zealand waters. New Zealand Fisheries Assessment Research Document. p.17 Australian Fisheries Management Authority 2005, Southern and Eastern Scalefish and Shark Fishery. Australian Government.
Review of fisheries biology for ribaldo (Mora moro) 14 Walker, T., Gason, A., & Koopman, M. 2007. SESSF scalefish abundance and spatial distributional trends from available ISMP data. Final report to Australian Fisheries Management Authority Project No. 05/1096. (February 2007). 199 pp. (Primary Industries Research Victoria: Queenscliff, Victoria, Australia).
Review of fisheries biology for ribaldo (Mora moro) 15