All posts by Jill Studholme

By Jill Studholme. Jill edits SCUBA News (ISSN 1476-8011), the monthly newsletter with articles on diving and marine science. She tweets as @SCUBANews. You can find her on Google+ at https://plus.google.com/+JillStudholme/.
Helmut Jellyfish

Strange marine animals found around the Canary Islands

Marine conservation group Oceana have found an amazing array of marine life in their expedition around the Canary Islands.

Oceana - Siphonophora

Siphonophora, photo © Oceana

Using ROVs (remotely operated underwater vehicles) down to 1000 m as well as scuba divers to shallow depths, they documented large colonies of deep-sea white coral, crystal aggregations of sponges, dense forests of black corals, oceanic puffers, giant foraminifera, carnivorous sponges and sharks, as well as many other biological communities and species in the south of the El Hierro Island.

Oceanic Puffers

Aggregation of Oceanic puffers (Lagocephalus lagocephalus lagocephalus) with reproductive purposes. El Desierto, El Hierro, Canary Islands, Spain. photo © Oceana

“Although there are some habitats that are specific to certain depths, in all dives and environments we have documented many different species, demonstrating the richness in biodiversity of southern El Hierro”, says Ricardo Aguilar, Research Director at Oceana in Europe. “With information gathered from this expedition, we intend to promote the creation of a marine national park in the southern part of El Hierro island; the first one in Europe.”

Nemichthys sp

Nemichthys sp, photo © Oceana

El Hierro boasts highly diverse and valuable marine habitats and species, which led Oceana to propose the protection of its waters in 2011. Earlier this year El Hierro became the first island in the world to use 100 percent renewable energies, making the island unique from an environmental point of view.

Carnivorous sponge

Carnivorous sponge photo © Oceana

As well as documenting the sea life around El Hierro, the expedition is exploring for the first time seamounts in the Eastern Atlantic. These have hardly ever been filmed before.

Brown-snout spookfish (Dolichopteryx longipes)

Brown-snout spookfish (Dolichopteryx longipes), photo © Oceana

The Canary Islands and their adjacent seamounts hold the most diverse elasmobranchs (sharks and rays) community of the whole European Union, with up to 79 species identified.

Bigeye thresher shark (Alopias superciliosus)

Bigeye thresher shark (Alopias superciliosus) photo © Oceana

Oceana was founded in 2001 and is the largest international organization focused solely on ocean conservation, protecting marine ecosystems and endangered species.

Vampire Squid

Vampire Squid, photo © Oceana

Sea urchin (Phormosoma placenta)

Sea urchin (Phormosoma placenta), photo © Oceana

Tripod Fish (Bathypterois dubius)

Tripod Fish (Bathypterois dubius), photo © Oceana

Sea Cucumber Elasipodida

Sea Cucumber Elasipodida, photo © Oceana

All photos copyright Oceana

Further Reading:
Oceana – Canary Islands Expedition 2014

SCUBA Fish Count

Silent divers count more fish

SCUBA divers underestimate the amount of life in heavily-fished areas, a study suggests.

Scientists from Australia compared fish counts by SCUBA divers—who produce noisy bubbles—and divers using silent rebreathers. They found little difference in counts between the two in Marine Protected Areas (MPAs), where the fish weren’t frightened of the divers. In more heavily fished areas though, the bubble-free divers recorded 48% more species and up to 260% greater fish abundance than the SCUBA divers.

snapper

Visual assessment by SCUBA divers is a commonly used method to gauge reef fish communities. However, the report in the journal Methods in Ecology and Evolution casts doubt upon its accuracy in some areas, saying that as fishing pressure increases so does the bias of the count.

The divers wearing rebreathers were able to get closer to the larger, most heavily-fished species which were very shy of divers in the non-protected areas. The researchers—Steven J. Lindfield, Euan S. Harvey, Jennifer L. McIlwain and Andrew R. Halford—recommend the use of this bubble-free diving system for surveys assessing reef fish populations, especially in areas where fish are heavily targeted by spearfishing. If fish behaviour isn’t taken into account, surveys using SCUBA could result in in the wrong conclusions when comparing fished and protected areas.

The surveys were carried out in Guam.

Further Reading:
Lindfield, S. J., Harvey, E. S., McIlwain, J. L., Halford, A. R. (2014), Silent fish surveys: bubble-free diving highlights inaccuracies associated with SCUBA-based surveys in heavily fished areas. Methods in Ecology and Evolution. doi: 10.1111/2041-210X.12262

Photo credit: Tim Nicholson

Scuba Challenge raising money for disability day

Gruelling Scuba Challenge on Tomorrow

Tomorrow is the SCUBA Challenge, where disabled and able-bodied divers will complete 64 lengths in the pool – fully kitted up – and 2 open water dives to raise money for Disability Day.

Organised by Dave Thompson, who sustained a spinal cord injury whilst playing American Football and has since been a full time wheelchair user with limited use in his left arm and none in his right arm or legs. As well as able-bodied divers, Dave is joined in this year’s challenge by three other disabled divers: two have spinal cord injuries and one has had a quadruple heart bypass. Proving the scuba diving is a fully inclusive hobby.

They are raising money to support the world’s largest ‘not for profit’ voluntary-led disability exhibition. If you would like to join Dave and the team, please email Dave on dave.thompson@5bp.nhs.uk. Alternatively you can donate at https://www.justgiving.com/scubachallenge2014/.

One of the divers is 22 year old ex-serviceman Tom Coleridge, a full time wheelchair user since being shot in Afghanistan in 2010. Tom’s injury left him paralysed from the waist.

The SCUBA Challenge day will start with an 18 m morning dive at Capenwray Quarry in Lancashire, followed by an afternoon 18 m dive at Eccleston Delph and finally late afternoon 64 lengths of the swimming pool at Woolston Leisure Centre, Warrington (UK).

Dave told us how he felt on a previous year’s challenge (and that one didn’t include an open water dives).

“For me it was a slow, slow and even slower pace. After ten lengths I felt a deep pain in my one good shoulder which was probably due to the weeks of training. I managed to stop a few time (under water) whilst John my dive buddy for the day adjusted my weights. But once into a rhythm the next thirty lengths flew by, and at forty five lengths John signalled that I should change my tank as I was low on air, I must admit that I was so knackered, I hadn’t noticed. As I surfaced briefly, my wife Pam handed me a drink, but just reaching for the bottle was excruciatingly painful. The stretching hadn’t done me much good; in fact my single arm long stroke was now reduced to a very small flicker type movement, but it kept me going between several rests lying on the bottom. At one stage I just wanted to close my eyes and go to sleep, thinking that I might wake up and it would be over.

But eventually John counted down the last few lengths from ten, and then somehow I saw one finger. This was it just one to go. One final push to the finish and as I surfaced everyone was standing around the pool cheering and clapping. As I hung onto the edge of the pool I remember seeing Simon’s face with a huge smile, and then Graham grabbed hold of my tank just as I was sliding back into the water. I remember looking around and feeling a huge sense of physical achievement, a sense that I hadn’t felt for twenty two years. One of the highlights of the day was swimming the last length with my son Gavin who was attempting a try dive. Ironically I finished at the opposite end to the pool hoist and had to swim back to get out. But on the way back John handed me a stud earring that had glistened at me each time I swam past it. It’s strange how something so small became a focus even though I was totally exhausted. My spirits were lifted as one by one everyone came forward as I handed out their certificates.”

scuba challenge for disability day
To donate, join in or find out more go to https://www.justgiving.com/scubachallenge2014/ or contact Dave on dave.thompson@5bp.nhs.uk

European eel

Ship noise slows eels and lets predators catch them twice as quickly

Eels are losing the fight to survive when faced with marine noise pollution such as that of passing ships, according to a study published in the journal Global Change Biology.

Scientists from the Universities of Exeter and Bristol that found that in the presence of ship noise, European eels (Anguilla anguilla) were 50% less likely to respond to an ambush from a predator, while those that did had 25% slower reaction times. Those that were pursued by a predator were caught more than twice as quickly.

Lead researcher Dr Steve Simpson, Senior Lecturer in Marine Biology & Global Change at the University of Exeter, said: “Our findings demonstrate that acute acoustic events, such as the noise of a passing ship, may have serious impacts on animals with direct consequences for life-or-death behavioural responses. If these impacts affect whole populations then the endangered eel, which has seen a 90% crash in abundance over the past 20 years due to climate change, may have one more problem to deal with as they cross busy coastal areas.”

When scientists played recordings of shipping noise to eels, the fish had higher stress levels and reduced right-left preferences.

The study highlights the importance of assessing the scale of impacts of the noise that now pervades many coastal environments.

The European eel is classified as ‘Critically Endangered’ by the IUCN Red List of Threatened Species. As well as noise pollution it faces loss of habitat, physical barriers to migration, problems with parasites and over-fishing.

Further Reading:
Simpson, S. D., Purser, J. and Radford, A. N. (2014), Anthropogenic noise compromises antipredator behaviour in European eels. Global Change Biology. doi: 10.1111/gcb.12685

Photo credit: David Perez (CC BY 3.0)

Hammerhead sharks

Shark Fin Sales Halved in China

Prices and sales of shark fin are falling in China by 50-70% according to a report by environmental group WildAid.

Around 7% of all sharks are killed every year. This exceeds the average rebound rate for many shark populations, meaning that if things don’t change they are condemned to extinction. Shark products include meat, skin, teeth and oil, but it is the higher market value of shark fins – primarily in China – that has driven the demand for these beautiful animals and their population declines. However things are changing. A campaign in China to raise awareness of the effects of buying shark products has been very successful.

Demand reduction can be very effective” says Peter Knights, Executive Director of WildAid. “The more people learn about the consequences of eating shark fin soup, the less they want to participate in the trade. Government bans on shark fin at state banquets in China and Hong Kong also helped send the right message.

The new report documents:

  • 82% decline in sales reported by shark fin vendors in Guangzhou, China
  • 85% of Chinese consumers surveyed online said they gave up shark fin soup within the past 3 years. Two thirds cited awareness campaigns with 28% citing the government banquet ban as a reason.
  • 24 airlines, three shipping lines and five hotel groups have officially banned shark fin from their operations

Up to 73 million sharks are killed for their fins. Of the fourteen shark species most prevalent in the shark fin trade, all have experienced regional population declines ranging from 40-99%, and all are classified as Threatened or Near Threatened by the International Union for the Conservation of Nature (IUCN)

In the Guangzhou markets, assumed to be the new centre of China’s shark fin trade, wholesale traders are now complaining of dwindling sales and falling prices. Retailers who were selling medium-sized shark fins for as much as US$642 per kilogram are now able only to charge half as much. One Guangzhou wholesaler commented that “shark fin is a dying business” and another is quoted saying that “Yao Ming’s commercial impact single-handedly smashed my business,” in reference to WildAid’s ongoing multimedia public awareness campaigns.

The sharks most commonly killed for fins are: tiger shark, great hammerhead, scalloped hammerhead, oceanic whitetip, thresher shark, blue shark, shortfin mako shark, bull shark, silky shark, dusky shark and sandbar shark.

Tiger shark

Although the report is good news for sharks, the shark fin trade continues, both legally and illegally. For example in March 2014, WildAid interviews with Belizean fishermen revealed they continue to get US$75 per pound (approximately US$165 per kilogram) for medium to large shark fin and, comparatively, only US$7 per pound (approximately US$15 per kilogram) for the meat. Evidence of locally protected nurse sharks being targeted for their fins was also noted. In April 2014, the Belizean Fisheries Department arrested two fishermen for the attempted illegal export of 73 dried shark fins and other marine products to Guatemala.

So, good news for sharks but still work to be done to save the sharks and their oceans.

Deep sea octopus

Deep sea octopus broods eggs longer than any known animal – 4 years

Researchers at the Monterey Bay Aquarium Research Institute have observed a deep-sea octopus brooding its eggs for four and a half years – longer than any other known animal. Throughout this time, the mother kept the eggs clean and guarded them from predators.

deep sea octopus
Deep-sea octopus (Graneledone boreopacifica) protecting her eggs. Photo credit: Robison et al (CC-BY)

Octopuses typically have a single reproductive period and then they die. Once a clutch of fertilized eggs has been produced, the mother protects and tends them until they hatch. In most shallow-water species this brooding period lasts between one and three months. Very little is known though about the maternal behaviour of deep-living species. In the cold, dark waters of the deep ocean, metabolic processes are often slower than their counterparts at shallower depths.

Every few months for the last 25 years, a team of Monterey Bay researchers led by Bruce Robison has used a remotely operated vehicle (ROV) to survey deep-sea animals at a research site in the depths of Monterey Canyon that they call “Midwater 1.” In May 2007, during one of these surveys, the researchers discovered a female octopus clinging to a rocky ledge just above the floor of the canyon, about 1,400 meters (4,600 feet) below the ocean surface.

Each time the researchers returned, they found the same octopus clutching the vertical rock face, arms covering her eggs.

deep sea octopus
Here she is again. Photo credit 2007 MBARI.

As the years passed, her translucent eggs grew larger and the researchers could see young octopuses developing inside. Over the same period, the female gradually lost weight and her skin became loose and pale.

The researchers never saw the female leave her eggs or eat anything. She did not even show interest in small crabs and shrimp that crawled or swam by, as long as they did not bother her eggs.

The last time the researchers saw the brooding octopus was in September 2011. When they returned one month later, they found that the female was gone. As the researchers wrote in a recent paper in the Public Library of Science (PLOS ONE), “the rock face she had occupied held the tattered remnants of empty egg capsules.”

Previously, the longest octopus brooding known was 14 months. The longest guarded incubation known for fish eggs is 4–5 months, by the Magellan Plunder Fish Harpagifer bispinis in Antarctic waters. For birds, the longest uninterrupted egg brooding is 2 months, by the Emperor Penguin. Among live-bearing species, elephants gestate for 20 to 21 months, frilled sharks carry their embryos internally for about 42 months, and the internal gestation period of alpine salamanders can reach 48 months before birth.

The prolonged brooding period for the deep sea octopus is a result of two factors, low temperature and the advantage of producing highly-developed hatchlings.

Further Reading:
Robison B, Seibel B, Drazen J (2014) Deep-Sea Octopus (Graneledone boreopacifica) Conducts the Longest-Known Egg-Brooding Period of Any Animal. PLoS ONE 9(7): e103437. doi:10.1371/journal.pone.0103437

Parrotfish in fishing net

Caribbean coral reefs gone within 20 years

Most Caribbean coral reefs may disappear in the next 20 years, if something isn’t done, a new report warns.

Caribbean corals have declined by more than 50% since the 1970s. But the good news is that the trend can be reversed. Restoring parrotfish populations and improving other management strategies, such as protection from overfishing and excessive coastal pollution, could help the reefs recover and make them more resilient to future climate change impacts. So says the report, Status and Trends of Caribbean Coral Reefs: 1970-2012, which is the result of the work of 90 experts over the course of three years. It contains the analysis of more than 35,000 surveys conducted at 90 Caribbean locations since 1970, including studies of corals, seaweeds, grazing sea urchins and fish.

The main problem faced by the reefs is the loss of grazers, like parrotfish in the region. Climate change, which has long been blamed for coral degradation does pose a serious threat by making oceans more acidic and causing coral bleaching, but the report shows that the loss of parrotfish and sea urchins has, in fact, been the key driver of coral decline in the Caribbean.

Sea urchin on caribbean coral reef
Sea Urchin

Disease led to mass mortality of the sea urchin in 1983 whilst over-fishing has brought the parrotfish population to the brink of extinction in some places. The loss of these species allows algae, on which they feed, to smother the reefs.

Parrotfish are missing from Caribbean Coral Reefs
Parrotfish, photo credit: Tim Nicholson

“Even if we could somehow make climate change disappear tomorrow, these reefs would continue their decline,” says Jeremy Jackson, lead author of the report. “We must immediately address the grazing problem for the reefs to stand any chance of surviving future climate shifts.”

The report also shows that some of the healthiest Caribbean coral reefs are those that harbour vigorous populations of grazing parrotfish. These include the Flower Garden Banks National Marine Sanctuary in the northern Gulf of Mexico, Bermuda and Bonaire, all of which have restricted or banned fishing practices that harm parrotfish, such as fish traps and spearfishing. Other countries are following suit.

Local decisions and actions can make a big difference to the reefs. Bermuda, for example, has 39% coral cover whilst most areas have less than 14%.

Reefs where parrotfish are not protected have suffered tragic declines, including Jamaica, the entire Florida Reef Tract from Miami to Key West, and the U.S. Virgin Islands.

“The rate at which the Caribbean corals have been declining is truly alarming,” says Carl Gustaf Lundin, Director of IUCN’s Global Marine and Polar Programme. “But this study brings some very encouraging news: the fate of Caribbean corals is not beyond our control and there are some very concrete steps that we can take to help them recover.”

Healthy coral
Healthy Coral, photo credit: Tim Nicholson

The authors also looked at the impact of invasive species like lionfish, but concluded that although they have “wreaked havoc in Caribbean fish communities…they pale in comparison to the introduction of the unidentified pathogen that caused the die-off of Diadema antillarum or the effects of “White-band disease” on acroporid corals.”

Lionfish
Lionfish, photo credit: Tim Nicholson

The authors of the report recommend adopting conservation and fisheries management strategies that lead to the restoration of parrotfish populations and so restore the balance between algae and coral.

Further Reading:
Status and Trends of Caribbean Coral Reefs: 1970-2012

Deploying Red Tide Detector

Sensors watch for Red Tides

This year an array of sensors are watching for harmful red tides in the Gulf of Maine.

The red tide is caused by the germination of dormant cysts of alga called Alexandrium fundyense, which produces a toxin that can cause paralytic shellfish poisoning. Another name for a red tide is “harmful algal bloom” or HAB.

Scientists have been monitoring red tides for years, so that they can warn people when problems are about to occur. They typically base their annual red tide forecast on the abundance of cysts in bottom sediments combined with a computer model that simulates a range of bloom scenarios based on previous years’ conditions. However, oceanographic conditions are changing which meant that the forecast for both 2010 and 2013 were inaccurate.

This year, then, researchers are using four robotic instruments called Environmental Sample Processors (ESPs) that measure bloom concentration and toxins at several spots along the Gulf of Maine and provide near real-time data on toxic algae which they transmit to shore. The ESPs are mounted to ocean buoys and will detect and estimate concentrations of algal species that cause red tides and one of the potentially fatal toxins they produce.

“The ESPs are not a replacement for state-run programs that monitor naturally occurring marine toxins in shellfish,” said Kohl Kanwit, Director of the Bureau of Public Health for the Maine Department of Marine Resources. “Instead, they provide valuable data on the algal cells and associated toxins in coastal waters, giving managers early warning and a more complete picture of the magnitude and distribution of HAB events.”

Further Reading:
Woods Hole Oceanographic Institute
What is a Red Tide?

Photo credit: Photo by Isaac Rosenthal, Woods Hole Oceanographic Institution & Northeastern University

Endangered Sawfish Strategy Launched

Plan to save sawfish – most endangered fish in the sea

The International Union for Conservation of Nature (IUCN) has released a global strategy to prevent extinction and promote recovery of sawfishes.

The strategy by the IUCN’s Shark Specialist Group was launched at the Sharks International conference in South Africa and coincides with announcements that two West Africa countries – Guinea and Guinea Bissau – are proposing the listing of sawfishes under the Convention on Migratory Species in November, which could significantly boost protections.

Sawfishes have been devastated worldwide by overfishing and habitat loss. “The sawfishes, revered for millennia by coastal cultures around the world, now face greater extinction risk than any other family of marine fish,” the strategy’s co-author, Dr. Nick Dulvy, said. “With this comprehensive strategy, we aim to reignite sawfish reverence and spark conservation action in time to bring these iconic species back from the brink” he added.

Sawfish are very large – reaching up to 7 m. These shark-like rays have distinctive, toothed, snouts from which they get their name. All five species are classified as Endangered or Critically Endangered on the IUCN Red List of Threatened Species. They live in coastal tropical and subtropical waters worldwide, including estuaries and river systems as well as the oceans.

“Although these species are perilously close to extinction in many regions, there are some fairly simple ways to help populations recover. For example, we know that sawfish can actually survive capture quite well if handled properly, and hence, basic education of commercial, subsistence, and recreational fishers is central to our conservation strategy,” said Dr. Colin Simpfendorfer, Professor of Environmental Science at James Cook University in Queensland.

The toothed rostrum (snout) makes sawfish especially prone to entanglement in fishing nets. As many live in estuaries, coastal development and loss of habitat is another factor that has depleted populations. Like other sharks and rays, their slow growth – taking 10 years to reach maturity – makes for a vulnerable population.

To compliment an existing ban on commercial international sawfish trade, the Strategy calls for national and regional actions to prohibit intentional killing of sawfish, minimise mortality of accidental catches, protect sawfish habitats, and ensure effective enforcement of such safeguards.

Further Reading:
IUCN

Sustainable fishing stamps

Stamping out over-fishing

For the first time, Britain’s Royal Mail has issued stamps championing an environmental issue – and that issue is sustainable fishing. Over-fishing has long been a problem – policy-makers don’t seem to understand if you take more fish out of the sea than can be replaced then you will run out. One way things might change is by consumers voting with their purses and choosing to buy only fish that can be caught sustainably. Research by the Royal Mail, though, has revealed that little is known by the public about which fish are in trouble and which we can eat.

Half of the species illustrated are fish that are at risk in UK waters: Common Skate; Spiny Dogfish (Rock Salmon); Wolffish; Sturgeon and Conger Eel. The other half are species from what are probably sustainable populations and suitable alternatives: Herring; Red Gurnard; Dab; Pouting and Cornish Sardine.

Professor Callum Roberts who acted as consultant for Royal Mail on the stamp issue said: “Marine protected areas that are off limits to fishing could recover endangered species like those on the stamps, as well as providing a boost to the fishing industry through recovered stocks. Only one thousandth of 1% of UK seas are fully protected from fishing at present. To bring back endangered fish species, we need a huge increase in the coverage of such protected areas.”

The Threatened Fish

Common Skate, Dipturus batis

Common Skate, Dipturus batis
The largest skate found in European waters, with females growing up to 285 cm. They can live up to 100 years. Previously widespread – as the name implies – they are now extinct in the Mediterranean and greatly reduced in range around Britain. Retaining and landing common skate is now prohibited in EU waters. Common skate is assessed as Critically Endangered.

Wolffish, Anarhichas lupus

Woffish, Anarhichas lupus
Wolffish live on the seabed. They do not reproduce until they are 8 to 10 years old. Modern fishing methods have severely reduced wolffish numbers, not just by catching the fish but also by destroying their habitat and breeding grounds with intensive, repeated bottom trawling.

Common Skate, Dipturus batis

Conger Eel, Conger conger
This massive fish can grow to almost 3 m (10 ft) long, the females often being bigger than the males. Congers breed only once in their lives, commonly when they reach 5 years old, after which they die. As they breed only once, just about all eels which are caught in fishing nets are juveniles which have not yet reached spawning age. They only become sexually mature during the journey to the spawning areas.

Spiny Dogfish, Squalus acanthias

Spiny Dogfish, Squalus acanthias
More commonly known in the fishmongers as Rock Salmon, the spiny dogfish is critically endangered. It is a long-lived, slow-growing and late-maturing species and therefore particularly vulnerable to fishing. Pregnancy lasts between 18 and 22 months, one of the longest recorded for any vertebrate, and they give birth to live young. Older females produce 10 to 21 pups, but younger ones (who are smaller than 1 m) produce less.

Sturgeon, Acipenser, Huso spp

Sturgeon, Acipenser, Huso spp
Although some sturgeon sold are farmed, those caught in nets should be avoided. According to the Marine Conservation Society (MCS) “The value of wild sturgeon caviar is so high that there is a substantial illegal fishery for sturgeon that is completely unregulated. Consequently many species are in rapid decline.

Fish that are OK to Eat

Pouting or Bib

Pouting or Bib, Trisopterus luscus
Called Pouting on the stamp but known to divers as Bib. A member of the cod family, matures at just 1 to 2 years and around 23 cm long. Pouting is considered an “under-utilised species”: the ones that fishermen don’t catch their full quota of; or they catch them but then discard the fish because no one wants to buy them. Can be used in recipes specifying white fish.

Herring

Herring, Clupea harengus
Herring is a familiar fish. Its sustainability depends on the methods of the fishery catching it. Look for certification from the Marine Stewardship Council (MSC) to show that the Herring were caught responsibly.

Gurnard

Red Gurnard, Aspitrigla cuculus
Gurnards are a non-quota species so are often discarded due to low market demand. If we eat these it will stop fish being wasted in this way. Avoid eating immature fish – those less than 25cm – and fresh fish caught in summer during the spawning season.

Sardine

Cornish Sardine, Sardina pilchardus
Look for MSC certified fish with the Blue tick logo on the package. The most sustainable sardine fishery are the Cornish boats using traditional pilchard drift nets. Sardines and pilchards are the same fish, the larger fish are known and pilchards and the smaller as sardines.

Dab

Dab, Limanda limanda
Dab is one of the most abundant fish in the North Sea and can be eaten instead of other flat fish like plaice.

Further reading:
Royal Mail
Fish online: a good site to find out about which other fish to eat or avoid from the Marine Conservation Society