Template:Short description Template:Use New Zealand English Template:Speciesbox Template:About
The New Zealand blue cod (Parapercis colias) is a temperate marine ray-finned fish<ref name="Carbines2004.a" /> of the family Pinguipedidae.<ref name="NZOR">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> It is also known by its Māori names, rāwaru, pākirikiri and patutuki, and by its other names in English, Boston blue cod, New Zealand cod or sand perch.<ref name="MPIname">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>
It is exclusively found in New Zealand, in shallow waters around rocky coasts to a depth of 150 m, though it is far more common south of the Cook Strait.<ref name="Carbine1998" /> It is bluish green to blue-black above with white toward the belly.<ref name="Paulin1989" /> Large examples are usually greenish blue in colour, while smaller ones are blotched in varying shades of brown.<ref name="Paulin1989" /> An adult may grow to 60 cm in length and weigh from 1.0 to 3.0 kg.<ref name="Hirt-Chabbert" /><ref name="JiangCarbine" /> It feeds mainly on small fish and crabs.<ref name="Russell">Template:Cite journal</ref> Blue cod is territorial.<ref name="Mutch" /> Spawning takes place in southern spring.<ref name="AylingCox" /><ref name="PankhurstConroy" /> Blue cod can also change sex from female to male.<ref name="Carbines1998'" />
It is an important recreational species in the South Island and is commercially harvested.<ref name="Paul.a" /><ref name="Paul.b" /> Blue cod populations are managed under New Zealand's fisheries quota management system, although they are becoming scarce in some small areas due to fishing pressure.<ref name="MPI2018" /> Annual catch range is between 2,000 and 2,500 tonnes.<ref name="MPI2014" />
IdentificationEdit
Parapercis colias are protogynous hermaphrodites, which means they have both female and male reproductive organs at the beginning and some females change sex to males later in their life.<ref name="Carbines.b" /> P. colias is a marine bottom dwelling fish that is found in coastal New Zealand waters.<ref name=MPI2018/> Their colouring varies on age and sex.<ref name="Paul.b" /> Juveniles start off being generally pale in colour and have two long dark stripes along the sides which will turn brown and barely distinguishable when they become middle-sized fish.<ref name="MPI2018" /><ref name="Paul.a" /><ref name="EoL" /> As they mature with a body length over 25 cm, both sexes would have a blueish-grey dorsal with a white underside.<ref name="MPI2018" /> Females have a tinge of orange and there is a trend for them to become green when they grow larger.<ref name="Paul.b" /> Brownish pigments can be found at the base of pectoral fin.<ref name="Paulin1989">Template:Cite book</ref> On the other hand, adult males have distinctive blue-grey colour coat with greenish sides<ref name="Paulin1998" /> and a golden brown line can be found above each eye.<ref name="Paul.b" /> Body length of P. colias is about 30–40 cm in general, but can up to 60 cm and their weight is 0.8–1.5 kg in general, but can up to 3 kg.<ref name="Hirt-Chabbert" /><ref name="JiangCarbine" /> Males tend to be larger than females. They can live up to 32 years old.<ref name=MPI2018/>
Heads of P. colias are prominent and rounded with scales.<ref name="AylingCox" /><ref name="Hirt-Chabbert" /><ref name="McDowall" /><ref name="Paul1993">Template:Cite book</ref> They have a plump shaped body covered with firm scales.<ref name="Paul.b" /> Above their non expanded cheeks are two large lateral eyes<ref name="McDowall" /> which can rotate independently, this allows them to see almost everywhere around them.<ref name="RH">Template:Cite book</ref> P. colias possess a terminal mouth<ref name="Paulin1989" /> with bulbous lips.<ref name="AylingCox" /><ref name="RH"/> Their pelvic fins are generally placed forward on the throat with brown dots appear underneath it.<ref name="Paulin1998" /> There is a single horizontal stripe where ten to twelve scales above across their side of the body.<ref name="Paulin1989" /> The anterior section of their dorsal fin is small and short,<ref name="Paul.a" /><ref name="Paulin1998" /> followed by fins with five short spines.<ref name="Hirt-Chabbert" /> In contrast their second dorsal is long.<ref name="Paulin1998" /> A key used in an article of Cantwell can distinguish P. colias from other parapercids.<ref name="Cantwell" /> Key features are listed below:<ref name="Cantwell">Template:Cite journal</ref>
- The outer row of lower jaw has eight teeth
- Dorsal spines longer to the posterior (rear end)
- Soft dorsal fins have 20 rays and anal fins with 17
- 10 to 11 scales are present from lateral line to base of first soft dorsal ray
- 23 to 26 counts of gill rakers
- Caudal (tail) fins have 15 branched rays that looks rounded but bi-lobed.<ref>Template:Cite book</ref>
Other characters of detailed skeleton structures (osteology) of Parapercis species can be found in an article written by Gosline.<ref>Template:Cite journal</ref>
Swimming bladder is usually present in osteichthyids,<ref>Template:Cite book</ref> it helps the fish to stay at a certain water pressure level (depth) without spending more energy. Swimming bladder in P. colias are absent.<ref name="Blackwell" /> They will automatically sink to the sea floor if they stop swimming; therefore, they are called bottom-dwelling or sedentary bottom-hugging species.<ref name="Thompson" /> Their body shape of having a flattened abdomen indicates this as well.<ref name="Thompson" /> Normally, P. colias use their pectoral fin to swim, their body muscles and tails fin are only involved in swimming when a sudden burst or speed is needed, this type of swimming character is called labriform.<ref name="Thompson" /> As a result, their pelvic fins, used as props when they are resting on the seabed,<ref name="AylingCox" /> are reduced and thicken.<ref name="Thompson" /> Due to their nature of being bottom-dwelling species, sand can clog their gills when they are resting.<ref name="Graham1997">Template:Cite book</ref> To remedy this, P. colias often hold their breath and open their mouths for a long interval like having a yawn to take good gulps of air every now and then.<ref name=Graham1997 /> Speaking of having a yawn, if you look closely you will notice that P. colias do not have palatine teeth<ref name="Paulin1989" /> and only have small teeth; however, you would not want to feel their sharp and well developed pharyngeal teeth near their throat like their prey.<ref name="Thompson" />
There are some other detailed morphological characteristics inside the body of P. colias that determine their taxonomy, such as the presence of a lentiform body (an ocular vascular structure) and others, are mentioned by Eastman.<ref name="Eastman">Template:Cite journal</ref>
DistributionEdit
Natural global rangeEdit
Pinguipedid fishes (Sandperches) are widely found in the southern Atlantic and Indo-Pacific regions.<ref name="Nelson">Template:Cite book</ref> However, P. colias is endemic to New Zealand.<ref name="Stroud">Template:Cite book</ref><ref name="Martin&Hine">Template:Cite book</ref>
New Zealand rangeEdit
P. colias is found from the shore to the shelf edge around New Zealand's entire coastline, but there are no records in either the Kermadec Islands or the Snares Islands / Tini Heke.<ref name="Francis">Template:Cite journal</ref> They are more abundant from south of Cook Strait<ref name="Paul.b">Template:Cite book</ref> and they are an iconic species for the South Island.<ref name=MPI2018>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> They are most common around Southland and the Chatham Islands.<ref name="Carbine1998">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>
Habitat preferencesEdit
P. colias can be found at 150 m in depth<ref name="Carbine1998" /><ref name="Hirt-Chabbert">Template:Cite book</ref><ref name="Paul.b" /> occupying bedrock outcrops on gravel<ref name="AylingCox">Template:Cite book</ref><ref name="Graham" /><ref name="Paul.a">Template:Cite book</ref><ref name="Paulin1998">Template:Cite book</ref> or sandy seabed.<ref name="BeentjesCarbines">Template:Cite journal</ref> These habitats with macro algae or Sponges are even more preferred.<ref name="BeentjesCarbines" /> Furthermore, their abundance in each habitat varies between age.<ref name="Mutch">Template:Cite book</ref><ref name="Paul.b" /> Juvenile are found more frequently in sponge gardens (more than 16m deep) dominated by orange finger sponges (Raspalia topsenti & Raspalia flaccida), large black massive sponge (Ancorina alata) and the small bright yellow clumps of Polymastia granulosa that provide more shelters and safer refuges, whereas adults are mainly found on reef margins<ref name="Thompson">Template:Cite book</ref> and deeper areas.<ref name="Paul.b" />
Since P. colias are generalists,<ref name="JiangCarbine">Template:Cite journal</ref> which means that they prey on various species instead of depending on only one species, habitats that are rich in diversity of species are also favoured by them. An example of this is the kelp forest which is often established on rock beds where it is also desirable for P. colias.<ref name="coleaylingcreese">Template:Cite journal</ref><ref name="FosterS">Template:Cite book</ref><ref name="Graham">Template:Cite book</ref> However, they can be also found in less species diverse habitats such as barren rock flats (4-12m deep) that are dominated by sea urchins grazing on algae.<ref name="Thompson" />
As mentioned before, P. colias can be found at 150 m in depth and was reported to be caught at 350m below the surface,<ref name="Carbine1998" /> other important aspects such as temperature, salinity and oxygen content in the ocean are often influenced by water depth.<ref name="McDowall">Template:Cite journal</ref> 766 samples were taken to determine the water temperature and chemistry ranges of P. colias<ref name="EoL" >{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> as listed below:
Temperature: 7.786 - 18.158 (°C) Nitrate: 0.205 - 18.689 (μmol/L) Salinity: 34.283 - 35.544 (PPS)Template:Clarify Oxygen: 5.121 - 6.587 (mL/L) Phosphate: 0.258 - 1.333 (μmol/L) Silicate: 1.911 - 7.690 (μmol/L)
Life cycle/phenologyEdit
Spawning and HatchingEdit
Multiple spawning events of a female P. colias occur throughout late winter and spring<ref name="AylingCox" /><ref name="PankhurstConroy">Template:Cite journal</ref> in the centre to the outer continental shelf.<ref name="Paul.b" /> Instead of a distinct spawning episode, their spawning is a continuous event that the eggs are released over time.<ref name="BrandtDunnBrouwer">Template:Cite journal</ref> One male can be spawning with different groups of female.<ref name="Hirt-Chabbert" /> Eggs could possibly drift 74 km away from the spawning site and hatch potentially after 116 hours.<ref name="Robertson1980" /> Young fish are found below 20 metres<ref name="Paulin1998" /> then move to shallow water in summer.<ref name="Paul.b" />
Age, Growth, Sex and MaturityEdit
Growth of P. colias is measured by the relationship between age and their body length.<ref name="BeentjesCarbines2012">Template:Cite journal</ref> P. colias are protogynous hermaphrodites,<ref name="Carbines1998'" >Template:Cite book</ref> when the length of P. colias reaches 410mm, 50% of the females are transitional.<ref name="Carbines.b">Template:Cite thesis</ref> Sex inversion occurs with the colour change from whitish with a brown band at both sides or an orange tinge to bluish colour with a blue green band.<ref name="AylingCox" /> Though sex inversion found to occur across a wide range of age and size, the cause of activating the sex inversion has not been well understood.<ref name="BeentjesCarbines" /> Studies have shown that the proportion of sex change decreases afterwards<ref name="Carbines.b" /> as the presence of males in the population would discourage sex change.<ref name="BeentjesCarbines" /> Hence, it is regarded as a response to the demographic structure in the population instead of a response to their size.<ref name="BeentjesCarbines" /> Another study indicated that blue cod is most fecund at the size which closes to the average size of the first maturity of males. It has been regarded as a sign of potential sex change by reducing egg production for saving the resource.<ref name="BrandtDunnBrouwer" /> Sex change is also not well described that the transitional gonads has different definitions.<ref name="BrandtDunnBrouwer" />
Their growth rate can differ due to food supply, water temperature and habitat as other fish do.<ref name="Paul.b" /> Sex can also influence the growth rate. Male grow faster and larger than female.<ref name="Carbines2004.a" >Template:Cite journal</ref><ref name="Paul.b" /> P. colias have the potential to grow up to 50 cm in length and weight 4 kg.<ref name="Ayling1987" >Template:Cite book</ref> Growth ring interpretation shows that they can live about 10 to 15 years,<ref name="Paul.b" /> but a study showed that the known maximum age of blue cod is 23 years old.<ref name="RodgersWing">Template:Cite journal</ref>
Maturity values are derived from the length of the fish.<ref name="BeentjesCarbines2012" /> Their growth rate varies between locations.<ref name="Mutch" /><ref name="Smith" /> For example, male can reach maturity when their length reached 10–19 cm (which is about 2–3 years old) in Northland, but in Southland the male needs to reach 26–28 cm (which is about 4–6 years old).<ref name="Smith">Template:Cite book</ref> Besides, males generally have a faster growth rate compared to females.<ref name="Carbines2004.a" /><ref name="Mutch" /><ref name="Paul.b" /> Both female and male P. colias are assumed to reach sexual maturity with the measuring of 28 cm.<ref name="Carbines.b" /> The maximum lifespan of P. colias is 32 years.<ref name="MPI2014" />
BehavioursEdit
Similar to other Parapercis species, male P. colias hold territories and their home range increases as the individual grows.<ref name="Mutch" /> Mutch found that they tend to hold large territories rather than but loose territories with small social groups that contain three to five females.<ref name="Govier" /> Though they hold stable territories, P. colias moves from time to time. In a study,<ref name="Carbine1998" /> P. colias can move with on average of 2.09±2.12 km, this could potentially be home range shifts.<ref name="RodgersWing" /> It is reported<ref name="Stroud" /> that P. colias emigrate from coastal to offshore waters in May of each year, this is thought to be a preparation for mating and spawning in early winter.
Thunder is known to agitate the fish. Reports since the 1950s have documented thunder activating blue cod's flight mechanisms, causing the fish to leap out of aquariums.<ref name="Secrets"/>
MigrationEdit
P. colias seem to be migratory at certain times in a year,<ref name="Paul.b" /> but little is known about their migration. Other studies indicated that they are relatively sedentary,<ref name="ColeVilloutaDavidson">Template:Cite journal</ref><ref name="MaceJohnston">Template:Cite journal</ref><ref name="RodgersWing" /> however, long-term dispersal has been suggested due to a record that one individual travelled 156 km over 20 months.<ref name="CarbinesMcKenzie">Template:Cite book</ref>
Diet and foragingEdit
Many fish species are generalists; thus, they are not limited by the predator-prey cycle.<ref name="Murdoch">Template:Cite journal</ref> P. colias is one of them.<ref name="JiangCarbine" /><ref name="Paulin1998" /><ref name="Paul.b" /> They have been recorded to have 52 taxa in their diet,<ref name="JiangCarbine" /> where adults are found to be more selective than juveniles.<ref name="Jones">Template:Cite journal</ref> It makes sense that when P. colias grows bigger, the variety of species in their diet also increases, this includes polychaetes, crustaceans, molluscs,<ref name="AylingCox" /><ref name="Graham" /><ref name="JiangCarbine" /><ref name="Jones" /><ref name="Stroud" /> Pisces,<ref name="Graham" /><ref name="Young">Template:Cite journal</ref> algae and even its own spawn!<ref name="Young" /> This means that P. colias are omnivores which "feeds on more one trophic level".<ref name="PimmLawton">Template:Cite journal</ref><ref name="Stroud" /> In short, you can say that they consume anything that is abundant and available locally.<ref name="Paul.b" /><ref name="Paul1993"/> Other than the development of the fish itself, what they consume differs from region to region<ref name="JiangCarbine" /><ref name="Sylvester">Template:Cite book</ref> and whether the area is fished or not plays an important role as well.<ref name="PimmLawton" /><ref name="JiangCarbine" /> One study<ref name="JiangCarbine" /> showed that oyster dredged habitat can reduce their prey diversity and have a negative effect on fish size. They usually stalk, seize and swallow their prey.<ref name="Paul.b" /> After being caught, they tend to regurgitate the stomach contents.<ref name="Graham" />
"Our Big Blue Backyard" is a documentary of New Zealand marine and shoreline species.<ref name="NHNZ">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> In the Chatham Islands episode, blue cod (P. colias) waits to feed on pāua, an endemic sea-snail that attaches itself on hard surfaces such as rocks, at its most vulnerable phases – when they move or are grasped up by a starfish using hundreds of tube feet.<ref name="NHNZ" /> They are also said to be voracious.<ref name="NHNZ" /><ref name="Stroud" />
Predators, parasites, and diseasesEdit
PredatorsEdit
Homo sapiens (humans) fish 2000 to 2500 tons of P. colias annually.<ref name="MPI2014" >{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> Natural predators include:
- Great white shark<ref name="NHNZ" />
- Benthic feeders, such as:
- Yellow-eyed penguins<ref name="Chilvers2014">Template:Cite journal</ref><ref name="Moore">Template:Cite journal</ref><ref name="Van">Template:Cite journal</ref>
- Dolphins<ref name="Federal">Template:Cite journal</ref>
- Sea birds, such as mollymawks<ref name="Govier">Template:Cite thesis</ref>
As many marine predators are generalists<ref name="Murdoch" /> there are many other potential predators not listed. P. colias are known to predate upon juveniles of their own species.<ref name="Young" />
ParasitesEdit
Hewitt and Hine<ref name="HewittHine">Template:Cite journal</ref> summarised the parasites found on blue cod including species in five main groups:
| Group | Species | Location on host |
|---|---|---|
| Protozoa |
|
|
| Digenea |
|
|
| Monogenea |
|
|
| Nematoda |
|
|
| Copepoda |
|
Blood sucking sea lice are also known to parasitise P. colias.<ref name="NHNZ" />
Disease and InjuriesEdit
No specific disease is found on P. colias, but some injuries have been recorded. Hooking injuries could cause tissue damage and possibly lead to mortality.<ref name="Carbines1999" >Template:Cite journal</ref> Despite having greater risk for parasitic, bacterial, or fungal infections, mortality after having a hook injury is often caused by blood loss rather than disease.<ref name="Meka" >Template:Cite journal</ref> An article suggests that small hooks cause more blood loss problems than big hooks to P. colias.<ref name="Carbines1999" />
Compared to other bony fish, swimming bladder in P. colias is absent,<ref name="Blackwell" >{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> this means that they do not suffer from barotrauma – an injury due expansion or eruption of the swimming bladder in fish, it is often caused by rapid water pressure change when rising from deep water to water surface.<ref name="Thorncraft">Template:Cite journal</ref>
In a human contextEdit
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Rāwaru was a valued traditional food for Māori who lived in the South Island, where the fish is more abundant.<ref name="Secrets">Template:Citeq</ref> Heads of rāwaru (P. colias, blue cod) were often given back to the sea as offerings to the god Maru before Māori return from fishing.<ref name="Best" >Template:Cite journal</ref>
The fish was an important species to early European settlers in New Zealand as a food source, and by the 1910s became even more popular in Australia, leading to the growth of the blue cod fishing industry in Southland.<ref name="Secrets"/>
History of the nameEdit
Blue cod (P. colias) is not a cod. The use of blue cod can date back to the time of Captain Cook.<ref name="Paul.b" /><ref name="Paul1993" /> Some early writers listed them as coal-fish which derived from unrelated European fish. However, this name is so widely used in New Zealand that it is unlikely to be changed.<ref name="Paul.b" />
Economic and population management issueEdit
Blue cod is well known by the public due to its commercial and recreational importance.<ref name="Paul.a" /><ref name="Paul.b" /> As mentioned before, we fish 2000 to 2500 tones of P. colias per year.<ref name="MPI2014" /> The value of P. colias as being the third popular recreational fishing species cannot be ignored,<ref name="MPI2018" /> this includes using their flesh as rock lobster bait.<ref name="Robertson1980" >Template:Cite journal</ref> It is estimated that the marginal willingness to pay for an additional P. colias is $1.61 per fish and the average willingness to pay is $24.46 per fish.<ref name="Williamson2000">Template:Cite conference</ref> It is estimated that in 1999, 1.2 million P. colias was harvested, of which 70% were from the South Island.<ref name="Williamson2000" /> Thus, Ministry for Primary Industries (New Zealand) has set minimum capture length and maximum capture limit of P. colias, which varies between areas mainly depending on abundance, to avoid depletion. For example, in the South-East area (of South Island from Clarence Point to Southland and extended to the Chatham Islands, New Zealand), no fish shorter than 30 cm can be taken and each fisher has a limit up to 30 fish per day.<ref name="MPI2018" />
To achieve sustainable fishing, it is crucial to persist healthy population structure with continuous monitoring and quotas set to date.<ref name="MPIs" >Template:Cite book</ref> However, as the largest fish in the population would be the male, males are often being caught and is thought to affect the females changing their sex earlier.<ref name="BeentjesCarbines" /> This is an emerging issue to all hermaphrodites.<ref name="Robinson" >Template:Cite journal</ref> Surprisingly, the sex ratio male to females of P. colias is about 5:1<ref name="Carbines.b" /> which is biologically implausible. This suggests that sex changes might not purely depend on fish length, but we cannot ignore the fact that fishery has changed the natural population composition of "P. colias". To understand the direct impact on P. colias despite population decline<ref name="BeentjesCarbines" /> further research is required.
In addition, the fundamental unit of concern of its management of population is the genetic structure that can lead to the reduction of the evolutionary potential for responding to environmental change, the increase of inbreeding risk and the force of selective genetic change.<ref name="Smith" /> Since a number of evidence indicated that blue cod are relatively sedentary,<ref name="ColeVilloutaDavidson" /><ref name="MaceJohnston" /><ref name="RodgersWing" /><ref name="Smith" /> the fishing pressure may lead to potential local depletion.<ref name="CarbinesMcKenzie" /> Recent studies showed that the genetic differences were significant between mainland List of islands of New Zealand population and Chatham Island population.<ref name="Gebbie" /><ref name="Smith" /> On the other hand, the differences within mainlandList of islands of New Zealand populations were limited while the pattern of the isolation by distance was detected.<ref name="Smith" /> Further research using microsatellite DNA markers suggested that some significant genetic differences between mainland population exist which indicate the potential long-distance dispersal, but the dispersal rate is too low to have demographic effect in the population.<ref name="Gebbie">Template:Cite book</ref>
ReferencesEdit
- {{#if:170968
| {{#invoke:template wrapper|wrap|_template=cite web|_exclude=id,ID,taxon
| url = https://www.itis.gov/servlet/SingleRpt/SingleRpt?search_topic=TSN&search_value=170968 | title = Parapercis colias | publisher = Integrated Taxonomic Information System }}
- {{#invoke:Cite taxon|main|fishbase|genus=|species=|subspecies=}}
External linksEdit
- Blue Cod Fishing and a link to the Blue Cod Fishing Regulations. Ministry of Fisheries.