«A. C. Alfaroa A. G. Jeffsb J. P. A. Gardnerc B. A. Bollard Breena J. Wilkind a Auckland University of Technology, Auckland, New Zealand b Two Fathom ...»
Green-lipped Mussels in GLM 9
A. C. Alfaroa
A. G. Jeffsb
J. P. A. Gardnerc
B. A. Bollard Breena
Auckland University of Technology, Auckland, New Zealand
Two Fathom Ltd, Auckland, New Zealand
Victoria University of Wellington, Wellington, New Zealand
Rutgers University, New Jersey, U.S.A.
New Zealand Fisheries Assessment Report 2011/48
Published by Ministry of Fisheries
ISSN 1175-1584 (print)
ISSN 1179-5352 (online)
Ministry of Fisheries Alfaro, A.C.; Jeffs, A.G.; Gardner, J.P.A.; Bollard Breen, B.A.; Wilkin, J. (2011).
Green-lipped Mussels in GLM 9 New Zealand Fisheries Assessment Report 2011/48.
This series continues the informal New Zealand Fisheries Assessment Research Document series which ceased at the end of 1999.
2 MUSSEL BIOLOGY AND ECOLOGY
2.2 Larval Development and Dispersal
2.3 Settlement Processes
2.3.1 Settlement Inducers – Physical
2.3.2 Settlement Inducers – Chemical
2.3.3 Settlement Inducers – Biological
2.4 Larval Abundance
2.5 Spat and Algal Abundances
2.6 Composition of Spat Material
2.7 Natural Movements of Spat Material
2.8 Adult Mussel Beds in GLM 9
3 ORIGIN AND BIOLOGY OF DRIFT MATERIAL
4 SPAT SUPPLY
4.1 History of Spat Collections at Ninety Mile Beach
4.2 Issues for Spat Supply from GLM 9
5 METHODOLOGIES TO INVESTIGATE POPULATION CONNECTIVITY OFMUSSELS AND ASSOCIATED SPECIES
5.1 Chemical Marking of Larvae
5.2 Elemental Signatures
5.3 Isotopic Signatures
5.4 Genetic Markers
5.5 Hydrodynamic and Larval Dispersal Modelling
5.5.2 Physical Processes
5.5.3 A Case Study
5.5.4 Combining Physical and Biological Processes
5.6 Oceanographic Information
6 METHODOLOGIES TO INVESTIGATE LOCATION AND EXTENT OFPOPULATIONS OF MUSSELS AND ASSOCIATED SPECIES
6.1 Remote Sensing
6.2 Local Knowledge
7 IDENTIFICATION OF KNOWLEDGE GAPS
8 ADDRESSING THE KNOWLEDGE GAPS
8.1 The location of source green-lipped mussel populations, and their relative contribution to the spat harvested in GLM 9
8.2 The location of source populations of hydroids, seaweeds and other debris, and their relative contribution to the spat material harvested in GLM 9....... 52
8.3 The status of populations of broodstock mussels, hydroids, seaweeds and sources of other debris that are important contributors to the arrival of mussel spat that is harvested in GLM 9
8.4 The functioning of the biological and physical pathways between populations of broodstock mussels and settlement material (hydroids, seaweed and other debris) and spat material harvested in GLM 9
8.5 The impact of spat harvesting in GLM 9 on natural coastal mussel populations, including potentially important broodstock populations........... 54 9 CONCLUSIONS
12.1 Appendix One - Semi-structured questionnaire for survey of local knowledge
12.2 Appendix Two - Detailed findings from survey of local knowledge.............. 71
EXECUTIVE SUMMARYAlfaro, A.C.; Jeffs, A.G.; Gardner, J.P.A.; Bollard Breen, B.A.; Wilkin, J. (2011). Green-lipped Mussels in GLM 9 New Zealand Fisheries Assessment Report 2011/48.
The green-lipped mussel (Perna canaliculus) is the most valuable aquaculture species in New Zealand, valued at $260 million of production in 2009. The industry is almost 100% reliant on seed mussels, or spat, caught from the wild. The majority of these wild seed mussels (more than 80%) are harvested from fisheries management area GLM 9, mostly from Ninety Mile Beach in the far north of the North Island. At certain times of the year, drifting spat material arrives in the surf zone just offshore from the beach. The material consists of detached seaweeds and hydroids, as well as other debris, to which the mussel spat are attached, often at more than a million mussels per kilogramme of material. An excess of 100 tonnes of mussel spat material is harvested from the beach each year and distributed to mussel farms around New Zealand.
Despite the enormous economic value to seafood production and sales that this small volume spat fishery underpins, there is remarkably little known about the source of these mussels in GLM 9.
Therefore, the purpose of this report is to review existing information about the GLM 9 resource, including the associated drift material, and to evaluate potential future research directions to best aid management of the resource. This includes evaluation of various scientific methods that could be used to determine the extent of the wild green-lipped mussel populations where the spat originates from, connectivity amongst these individual populations and connectivity between these populations and the supply of harvestable spat in GLM 9.
The review has identified five significant knowledge gaps in the green-lipped mussel fishery in GLM 9 and recommends corresponding research avenues in order to address each of these gaps.
These five knowledge gaps are recommended as five key topic areas for future research to guide the management of this important resource in the following order of priority.
1. The location of source green-lipped mussel populations, and their relative contribution to the spat harvested in GLM 9.
2. The location of source populations of hydroids, seaweeds and other debris, and their relative contribution to the spat material harvested in GLM 9.
3. The status of populations of broodstock mussels, hydroids, seaweeds and sources of other debris that are important contributors to the arrival of mussel spat that is harvested in GLM 9.
4. The functioning of the biological and physical pathways between populations of broodstock mussels and settlement material (hydroids, seaweed and other debris) and spat material harvested in GLM 9.
5. The impact of spat harvesting in GLM 9 on natural coastal mussel populations, including potentially important broodstock populations.
1 INTRODUCTIONAlthough the GLM 9 commercial fishery is of only a comparatively small size and value, it is the major source of mussel seed, or spat, for an aquaculture industry with more than $260 million of sales in 2009. The endemic green-lipped mussel, Perna canaliculus, is now the single most important seafood export species for New Zealand by value ($202 million in 2009), and this industry employs the equivalent of 2500 people (Ministry of Fisheries 2010). The mussels are sold under the trade name Greenshell, and are mostly exported to North America and Europe.
The industry has grown relatively quickly since its origins (Figure 1) and is currently planning for significant growth in order to meet the aquaculture sector growth target of $1 billion of production by 2025 (Figure 2) (New Zealand Aquaculture Council 2006).
Figure 2: Projections of future value of aquaculture production of Perna canaliculus in New Zealand based on two scenarios – continuation of existing mean growth rate, or higher growth rate associated with meeting the aquaculture sector growth target of $1 billion of production by 2025 (New Zealand Aquaculture Council 2006).
There are 1018 authorised mussel farms in New Zealand, mostly concentrated in the Marlborough Sounds and Coromandel areas (Ministry of Fisheries 2010). Currently, the Greenshell aquaculture industry is almost 100% reliant on seed mussels collected from the wild, with only a small volume being supplied from hatchery production. The largest supply of mussel spat for aquaculture is from harvesting over 100 tonnes of spat a year in GLM 9 (more than 80% of all spat used by the industry), with the balance mostly caught on spat catching ropes in Golden Bay and Marlborough Sounds.
Mussel farmers, particularly in the Marlborough Sounds, like to use a combination of spat from Ninety Mile Beach and Golden Bay for their farms, because the breeding cycles of these mussel populations appears to be different allowing for an extended period for harvesting mussels with full gonads (commonly referred to as “fat” mussels). Mussels grown from spat sourced from GLM 9 tend to fatten and spawn from around August until January, whilst those mussels grown from Golden Bay spat fatten and spawn later, usually starting around January and ending later in the summer.
Almost all the spat harvested from GLM 9 is taken from Ninety Mile Beach in the Far North, where it occasionally washes into shallow waters along the beach. Once in the surf zone, it is easily collected by hand in scoop nets, although one major harvester also uses a mechanical harvester consisting of a large scoop net mounted on the front of a tractor that can be driven into the water. The spat material is loaded onto trailers and towed off the beach to a nearby depot, where the material is sorted to remove debris and material not covered with mussel spat. Commercial harvesters often return up to 50% of the harvested material to the beach after sorting (Ministry of Fisheries 2004).
Figure 3: Spat and seaweed held next to farm line with a degradable stocking (Photo by A. C. Alfaro).
Mussel larvae originate from adult mussel beds then settle upon filamentous substrates (predominantly seaweed and hydroids) in a process called primary settlement. These primary settlers ntly then actively drift away from these substrates as juveniles (1 mm) to settle upon rocky substrates (1–2 (secondary settlement) where they can then grow to adults. The spat industry at Ninety Mile Beach spat relies upon primary settlers attached to seaweed or hydroids being transported and accumulated along the seafloor and being cast up on the beach, from where they are harvested. The locations of source adult mussel beds and primary settlement substrates as well as the details of transport mechanisms of both larvae and primary settlers are largely unknown.
Previous work has demonstrated that mussel juveniles have a strong selectivity of attachment for these natural filaments (Buchanan & Babcock 1997; Alfaro & Jeffs 2002), and the attachment process is determined by the physical structure (Alfaro & Jeffs 2002, 2003), chemical composition (Alfaro et al. 2006; Young et al. 2008), and bacterial biofilms (Ganesan et al. 2008; Ganesan et al. 2010) of the substrates.
Figure 4: Re-seeding mussel juveniles on ropes surrounded by degradable stockings (Source: Jenkins 1985).
Although macroalgae and hydroids provide a critical primary settlement substrate for mussel larvae, little is known about the potential sources and turnover rates (sustainability) of these macroalgae and hydroids, the mechanisms that dislodge and transport them, and their life span in the water before and after mussel larvae settle upon them. Thus, it is important that future investigations answer questions about the location, size and distribution of these macroalgal and hydroid populations, the source of the associated debris and their combined role in mussel spat transport and arrival to coastal areas. Most importantly, still largely unknown is the location of the mussel broodstock populations that supply the large quantities of spat harvested in GLM 9 and which are a significant basis for producing this burgeoning aquaculture product.
This report reviews a range of methodologies to investigate population connectivity of this greenlipped mussel spat resource, and identifies knowledge gaps so that future research may be targeted in the most appropriate and beneficial areas. The Ministry of Fisheries intends that this review would help to facilitate the direction for future management and research activity, particularly given the potential demands on the resource with further expansion in the mussel aquaculture industry, whilst also recognising that the spat resource also supports an important local non-commercial fishery.
1. To determine the best method(s) for investigating population connectivity of the green-lipped mussel resource and associated algal species at Ninety Mile Beach and adjacent coastal areas (GLM 9).
1. Undertake a desk-top study to identify, review and evaluate various scientific methods (e.g., acoustic mapping, aerial photography, 2-dimensional hydrodynamic modelling, elemental fingerprinting, side-scan sonar swath mapping) that could be used to determine the extent of and relationship between populations of green-lipped mussel at Ninety Mile Beach and adjacent coastal areas.
2. Identify potential knowledge gaps in the green-lipped mussel fishery in GLM 9 and evaluate future research directions to best aid management objectives.
2 MUSSEL BIOLOGY AND ECOLOGYThe mussel genus Perna differs from the more diverse genus Mytilus by its geographic distribution and by morphological characteristics, such as position of muscle scars, soft tissue morphology, and shell colouration (Siddall 1980; Wood et al. 2007). There are three species in the Perna genus. Perna canaliculus (Gmelin 1791) is endemic to New Zealand, while P. perna (Linnaeus 1758) is found throughout South America and Africa, and P. viridis (Linnaeus 1758) is present in the Indo-Pacific.
In New Zealand, P. canaliculus is distributed widely throughout the three main islands (Figure 5), but is more common in the warmer northern parts of the country (Powell 1979). Dense beds of up to 100 individuals m-2 can be found in northern coastal areas (Stead 1971; Flaws 1975; Hickman 1991), which can include rocky reefs, wharf piles, and soft bottom habitats (Morton & Miller 1973).
Intertidal (mid-littoral) populations are limited by aerial exposure (Paine 1971; Kennedy 1976;